SprintTimer Guide

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How does Photo Finish work?
Each image slice is a picture of the finish line at a specific point in time. The composited image, therefore, consists of a series of narrow images taken over a period of time. Moving horizontally in the image thus means standing at one point and moving in time. More detailed information can be found here: sprinttimer.se/blog
How accurate are the measurements?
The accuracy of newer iPhone/iPads with at least 120 fps frame rate is usually better than +-0.01 s. On older devices, it is within 0.03 s. More details can be found in the SprintTimer blog.

The first six results are from one device with direct sound input. The seventh is with two devices and Start Sender.

With a manual start, where the accuracy of the absolute time is low (0.1-0.2 s off), the difference between the runners is still accurate within 0.01 s.

Can I display 1/1000 s?
Yes, double tap on the time display in the photo finish view. It will also affect the times saved on the image. Only remember that the absolute time is not accurate down to 0.001 s. But that it can be used to time the difference between two close racers with reasonable accuracy. The rules in Track & Field say that you should only present results with 1/100 s accuracy.
How do I improve the image quality?
  • Try to stand higher than the runners and film down. This will minimize the risk that they obscure each other.
  • Hold very still, or preferably, put the iPhone/iPad on a stand. This improves both image quality and accuracy.
  • Adjust the slice width so the racer looks as normal as possible (arms and legs that move faster or slower than the body may still appear stretched out or compressed).
  • If possible, try to get a smooth and even background.
  • Good light conditions are essential to reduce motion blur and increase image quality. Check the exposure time in the preview. If it drops below 1/200 s, there might be some blurring.
  • Newer devices record with a higher frame rate, e.g. 120 or 240 fps (see more below).
At what frame rate is Photo Finish recorded?
Photo Finish uses the highest frame rate possible on your device:
iPhone 6 and newer, iPhone SE,
iPad Pro
240 fps
iPhone 5s, iPad Air 2,
Mini 4, iPod 6
120 fps
iPhone 5 & 5C,
iPad Air & Mini, iPod 5
60 fps
Older devices 30 fps
A high frame rate enables more narrow slices resulting in an image with less "ghosting" and reduced risk to miss parts of the body, especially at fast races and when standing close by. A high frame rate will also give a cleaner background making the runners easier to see and mark. Finally, it will also lessen the problem that runners in different lanes requires a different slice width since they move with a different speed relative to the camera.

Can SprintTimer be used to set official records?
No, mobile operating system (iOS, Android, WM etc) is the real-time, interrupt free system required to guarantee a 100% reliability down to a 0.001 s.
Why is the maximum recording time 300 s?
The rendering and scrolling times of the final image will be impracticably long otherwise. The pause button, however, can be used to cover longer finishes. If that not is enough, you can use Video Finish.
How do I handle very large finish images?
Navigate through the image: Rotate the device left and scroll with the slider or by swiping until you find a competitor. Then rotate back to portrait and mark the image.

It is usually not possible to save a long finish as one image due to memory limitations in the iPhone/iPad. The problem can be reduced by scaling the image in the save dialog. You can also crop the image by rotating left and set crop marks. It is no problem to save the finish in several pieces by first setting crop marks around some competitors and save. Then set new crop marks and save again.
How do I save the times for each competitor?
The results are generated by the time lines set with the Mark button. They are saved and can be emailed from Results on the main page. The email will comprise all the results from the same day, eliminating the need to email after every single race. If you have a start list in the Start Set up, the names are also added to the results.
How does SprintTimer compare to high-end photo finish equipment?
   SprintTimer  Prof Photo Finish
 Technique  Image slices  Image slices
 Frames/sec  240*  >1000
 Accuracy  0.005s-0.02s*  0.001s
 Race time  Unlimited  Unlimited
 Recording time  300 s  Unlimited
 Saved image height 1280 - 1920 px  500 - 2000 px
 Start  Manual/sound  Electric/start gun
 Lens  Wide/Normal**  Tele (better)
 Cost  $3-$6  > $5 000
*Depends on the iPhone/iPad used, newer is better.
**On iPhone 7+,8+,X. Others with extra lens.
Can I use SprintTimer in landscape view?
The finish view can be viewed in landscape*. Rotate the iPhone left (home button to the right) for better overview and faster scrolling. Rotate back for a closer view with higher accuracy. The landscape view can also be used to indicate how the image should be cropped when saving.

However, recording video in landscape would reduce the resolution by almost 50% and have other disadvantages as well. The rest of the app is therefore in portrait view.

*Remember to turn off the rotation lock in the control panel or the settings app.
What are the differences between saving an image, or the base video?
SprintTimer records the finish in the form of a 150 pixels wide video, that is the base video. The video contains accurate time information about every recorded frame. After the race, that video is read frame by frame, and each image is cropped and blended to the final photo finish image. When you save the image the full timing information for every slice is no longer available. When you play back a saved image, the time display will usually show close to the correct time, but there might be small discrepancies.

For accuracy reasons, you must, therefore, add time lines directly after the race, or if you don't have time to mark it, save the base video and add the time lines later. Do not save an image without time lines. A saved image cannot be processed and re-saved.

You can trust:
  • The time display when scrolling a base video
  • The time lines imprinted on an image created from a base video
You can not 100% trust:
  • The time display when viewing a saved image (look at the imprinted lines instead)
Saving the base video will give you full flexibility to recreate the photo finish at a later stage. Note that the "Previous race (back up)" is a base video.

Base videos are saved in the app and can be deleted from the base video list. Photo finish images are saved in the Photos app and can be deleted there as well as from the list.


Can I use Video Finish to time laps?
Yes. First ad a start list with names, number or other id:s. Place the iPhone/iPhone at the finish line and let it register all passages. Mark the video and tap Split for every passage until the finish where you tap Mark as usual. You can now export a CSV file with both split and final times. You can also view them if you go to the results page for that race and tap Views and choose Show split times.
What are the differences between saving an image, a processed video and the base video?
SprintTimer records a video frame each time motion is detected, that is the base video. The video contains accurate time information for every frame. When you save images or a processed video the times are imprinted on each frame, but the full timing information is no longer available. For accuracy reasons, you must, therefore, add the marks directly after the race, or if you don't have time, save the base video and add the marks later.

There is no difference regarding information or accuracy when saving images or a processed video, so you can pick the one you find most convenient.

Saving the base video will give you full flexibility to recreate the photo finish at a later stage. Note that the "Previous race (back up)" is a base video.

Base videos are saved in the app and can be deleted from the base video list. Processed videos are saved in the Photos app and can be deleted there as well as from the list.

Can I use Video Finish in front of the finish?
Yes, it is possible. Set the detection zone to Custom in the finish setup. Go to the preview and pinch the zone so it becomes low and wide. Then drag it to the lower part of the view, just above the finish line.

This will make it easier to identify the competitors, but might make it harder to see exactly when they pass the finish line.
Why is the frame rate limited to 60 (30) fps?
Video Finish uses a so-called ”non-binned” video which gives the best image quality. And that is limited to 30-60 fps depending on device. A higher frame rate would also result in a huge amount of images to step through. Since video finish mostly is used for longer races, getting the exact 1/100 second is seldom necessary. So often, low frames rate like 10 fps are more practical. A low frame rate will also make the motion detection more sensitive.

However, if you do need very high accuracy in Video Finish you can use the ”Dual mode” to interpolate between images and get the right 1/100 s.
Why are some competitors not detected and recorded?
When SprintTimer uses motion detection, it captures a video frame and calculates the color distribution within the detection zone. Then it captures the next frame, does the same calculation, and compares the two. If the difference is large enough it assumes that there has been a motion and saves the frame. If the object is small, or moves slowly, the changes will be small. A runner far away is small and moves slowly (fewer pixels will change) and is therefore easily missed. A high frame rate also makes the changes smaller and therefore makes the detection less sensitive.

So if you are experiencing missed competitors:
  • Move closer, 2-4 m is a recommended distance for cross country runners.
  • If you are unable to get close enough, go to the preview and zoom in to get the competitors to better fill out the frame.
  • In the preview, you can also increase the detection sensitivity.
  • Lower the frame rate, you seldom need 60 fps, unless you are dealing with very fast objects. If you want to increase the accuracy of the timing you can use the Dual mode when evaluating the race.
  • In extreme conditions, consider turning off the motion detection.
Remember that the motion detection is a convenience in order not to get too many frames, not fundamental to the timekeeping.


How do I start the clock from a distance?
Say that you, for example, are timing a 100 m sprint and have a starter with a gun at the start. You then have several options to start the clock in SprintTimer at the finish:
  1. Sound via cable. Make a long microphone extension cable and place a microphone (e.g. an iPhone headset) close to the starter. This is the most stable and accurate method to start the clock. You can find tips on how to make a cable in the SprintTimer blog
  2. Sound via Walkie Talkie. Place one Walkie Talkie close to the starter and one close to the iPhone/iPad and let the sound trigger the start of the clock. This is a common set up that gives good accuracy and is usually the best solution for very long distances, e.g. in rowing and kayaking.
  3. With two devices and a WiFi network (existing or temporary router) you can use Start Sender. With a good network the accuracy is very close to a sound cable. Tips about setting up a temporary router in the SprintTimer blog
  4. Hand/Mic. You start the clock manually, but the sound is recorded at the same time and is used to correct the time. Ir requires some extra steps after the race, but gives much better accuracy than a manual start.
  5. Manual start. Easy to use, but gives the lowest accuracy.
How do I make a count down in Self Start?
You can only have two commands separated by one time. However, by putting a double minus sign in the text, you can introduce a small pause. So a countdown from five would look like:

The pauses will be even longer if you lower the voice speed (but the voice will sound more sluggish).
Can I use Bluetooth speakers/headsets in Self Start?
Yes, connect your Bluetooth device in the settings app. Turn on Bluetooth in the start set up. If you have problems hearing the sound, open the control panel while in SprintTimer a tap the "sound out" symbol in "Music". Check that the headset is chosen.

Note: Bluetooth speakers should only be used for training. The Bluetooth connection can introduce a delay in the sound, sometimes up to 0.2 s, but it can be also be less depending on the equipment and the situation. So there will be an error in the times recorded, and there is no way to tell how large that error is.
How do I set up SprintTimer as timing gates?
Place a device with Start Sender at the first line and set the clock to start on Motion. Place the second device with Motion Finish on the finish line. Set it to start detecting after a certain time and set auto finish to On. Sync the devices. Tips about sprint testing in the SprintTimer blog
Can I measure reaction time?
Yes, if you have SprintTimer Pro you can use an Apple Watch or an iPhone with Start sender. You can read more in this blog post.
Can I have more than one device connected to Start Sender?
Yes, by turning on the "Multiple devices" switch in the set up you can attach several iPhones and iPads running Photo/Video Finish to one Start Sender. Just remember to sync them one at a time.
How can I improve network latency?
Latency is the delay that occurs in all networks when sending a signal from one device to the other. The latency affects the accuracy of the clock synchronization, and thus the timing. SprintTimer sends many synchronization calls between the devices (the round trip time of the last call is shown by the latency bar). But the app only uses the ones with low latency (called sync latency). It is, therefore, no problem if the latency bar jumps up and down, as long as the average sync latency is low (preferably less than 10 milliseconds).

After the synchronization, the latency will not affect sending a start signal, so an occasional red latency bar is of no consequence. The accuracy when using Start Sender on a low latency network is close to that of a direct sound input (see accuracy under Photo Finish above)

Some tips if the latency is high:
  1. Wait a few minutes to see if the sync latency drops.
  2. Disconnect and start the synchronization again.
  3. Try to connect to another network (i.e. 5 GHz instead of 2.4 GHz). Check that both devices are on the same network.
  4. Restart the router.
  5. Change the network channel if there are other networks in the area.
Where can I get Start Sender for Mac OS?
You can download it at sprinttimer.se/startsender. Start Sender for Mac OS is free, but requires that you have bought Start Sender in SprintTimer.
Does Start Sender require Internet access?
Direct mode requires a WiFi network, but that network does not have to be connected to the Internet. Over short distances (<30 m) it doesn't even require an external network.

Cloud mode requires Internet access, but no WiFi.
How accurate is Start Sender?
Since there are multiple devices with different clocks involved, Start Sender can add a small error to the timing. In direct mode it can be deduced from the sync error. If the average latency is less than 10 ms the error is negligible.

In cloud mode the error might be a little larger since the devices must sync individually against a server and over a network with higher latency. But tests have shown that the error over a good 3G or 4G network is less than 0.02 s.


Why isn't my exported results separated into columns in the spreadsheet?
CSV is not a well-defined standard and the implementation varies between spreadsheets and regions. While it mostly works OK in English speaking countries there can be problems in others. SprintTimer tries to follow the common practice, but you might, for example, need another separator.

The CSV-formatting can, therefore, be configured. Go to Results: Results List and pick a race. Then tap Set Up and change the parameters to get the format you want.

Can I use other cloud solutions like DropBox?
Yes, you can work directly with DropBox, Google Drive and Microsoft OneDrive through the Files app. Download the respective app and log in to your account. You can now pick a file if you go to Start Lists and tap "Import". When exporting you also get to choose any folder in iCloud, DropBox, OneDrive or Google drive.
Can I use SprintTimer with meet manager software?
Yes, the Results Manager can import EVT-files (Lynx event) and export LIF-files (Lynx results) that many meet managers can handle. For example EasyWare (short video clip) and SportsTracker (two videos).


The app is freezing, stops recording etc, what do I do?
This is not normal* and could be caused by a conflict in you specific device/system. Some steps that might fix this are:
  • Restart your device. Turn it off with: Settings app> General> Shut Down. Or use the button combination for your device. Then press the sleep/wake button to restart.
  • Remove the app and install it from the app store again. Note: This will remove saved base videos and results, so back up those first. Reinstalling the app doesn't cost anything
  • Do a factory reset of your device. This should be done as a last resort since it might involve substantial work. Do a back up first!

*SprintTimer has been running hundreds of consecutive timing sessions over several hours on different devices without any problems.

How do I prepare my iPhone/iPad for an important race?
Normally you can just open SprintTimer and start timing. For an important race, however, where you want to assure the maximum stability of your device, there are some steps you can take:
  1. Restart the device, e.g. from the settings app. This clears out the memory and any app lurking in the background.
  2. Turn off 'Background App Refresh' under General in the settings app
  3. Set an iPhone to 'Flight mode' to avoid incoming phone calls at a critical moment. If you use Start sender you then have to turn on WiFi, and if needed, Bluetooth.
Can I close SprintTimer while timing?
SprintTimer normally uses a processor clock with high accuracy. This is clock is running as long as the device is active (i.e. you can temporarily put SprintTimer in the background). If you put the device to sleep, however, that clock will stop. During very long races it can be useful to put SprintTimer to sleep to save energy. The app, therefore, uses a combination of other clocks as a backup.

You have started the clock but not the recording:
If you put SprintTimer to sleep when you have started the timer (but not the recording) it will automatically switch to the backup clock. The accuracy of the total time will be within a few hundredths of a second, and the difference between the racers will still have a 0.01 s accuracy.

The recording has started:
You should NOT leave SprintTimer while you are recording a finish. Setting it to pause does not help (the recording is still running, but no frames are captured).

Can I time multiple races at the same time?
Yes, if you have an extra clock and the last competitor in the first race finishes before the winner of the second race.

Time the first race as usual. At the start of the second race, start a separate clock. When all participants in the first race have finished, process the finish and return to the start view. Look at the extra clock. Pick a time ahead of the displayed time and enter that as the "offset time" in the start set up. When the extra clock reaches that time, start the clock in SprintTimer.

What can I do if I forgot to save the image, or if something unexpected happened?
If you want to recreate the last race, go to Results: Previous race. That will open and render a backup base video.
Can I use add-on lenses?
Yes, add on lenses do not affect the timing. The standard iPhone/iPad lens is pretty wide (unless you have an iPhone 7+, 8+ or X) and not ideal when there are different lanes, or the finish line is far away. An additional 2x-3x tele lens could, therefore, be very beneficial for track, and 8x-12x tele lenses have successfully been used for water sports like rowing and canoeing (see the image). Some cheaper tele lenses can be a bit blurry at the edges when taking photos, but that is less of a problem for Photo and Video finish where only the central part is essential. More info is found at the SprintTimer blog

How do I display Photo/Video Finish on a large monitor?
The iPhone/iPad screen can be mirrored on an external monitor, TV, or projector. Since SprintTimer runs in portrait view, it will only use a small part of the monitor. When presenting the Photo Finish image, however, a special routine allows it to use the full screen. See this blog post for more details.
Can I use a second iPhone/iPad to analyze the finish and create results?
Yes, if you transfer the base video to the other device. You can either upload the video to iCloud, or airdrop it directly into SprintTimer on another device. The transfer can be done either from the Save dialog in the finish view, or from the base video list in Results.
Are the guides available on-line?
Yes, you can find them at sprinttimer.se/support
Will there be an Android version of SprintTimer?
I have currently no plans for Android versions of any of my apps. The reasons are:
  • I am a single developer doing everything (from design to programming), so keeping all my apps up to date with new phones and iOS versions is challenge enough.
  • It is more fun to develop new apps and improve the current ones, rather than repeating everything in another programming environment.
  • One app that has been converted to Android by some partners, but the sales was much lower than for the iOS version (it seems that Android users don’t buy apps).


Do I have to pay separately for all my devices?
No, if you, for example, buy SprintTimer Pro on your iPhone, you can open the pro page on your iPad tap the Restore button (provided that you have the same App store account on both).
I have problems restoring, what do I do?
  1. Check that in-app purchases are allowed in the Settings app.
  2. Check that you are logged into iCloud
  3. Log out of the app store in the settings app. Then try to restore. You should then get a login dialog.
  4. Restart your device.
  5. Remove SprintTimer and install it from the app store again (remember to first export base videos and results that you want to keep).
What happens if I stop subscribing to SprintTimer Pro?
You will no longer have access to the Pro features. But you can still use all the functionality that comes with the basic SprintTimer.
Can I continue to use my "old" Start Sender and Results Manager if even I don't subscribe?
Yes, if you have previously bought the stand-alone SS and RM they will work as before. However, you will not benefit from the updates that have been added since v. 14.0, nor to upgrades that eventually are included in SprintTimer Pro. If you upgrade, you will get the first year free.

SS and RM are no longer available for purchase, but they can still be restored through the Restore-button if need be.
What does SprintTimer Pro offer in addition to the "old" Start Sender and Results Manager modules?
  • Share Photo finish images with the on-line SprintTimer viewer.
  • Measure start reaction with Start Sender and Apple Watch
  • Copy and paste start lists from spreadsheets
  • Show the running time on an external display
More SprintTimer Pro specific features will be added in future updates.
How do I unsubscribe?
  1. Launch the Settings app.
  2. Tap iTunes & App Store.
  3. Tap on your Apple ID.
  4. Tap View Apple ID.
  5. Tap Subscriptions.
  6. Tap on SprintTimer Pro.
  7. Tap Cancel Subscription.
  8. Tap Confirm when prompted to confirm that you want to cancel your subscription.
The subscription will renew automatically if you don't cancel at least 24 hours before the next subscription period.
Why is SprintTimer Pro not a one-time payment?
There is a lot of effort going into continuously improving SprintTimer. So far, there has been over 100 updated versions of the app. The App store doesn't allow for paid upgrades, so a subscription is the only model that allows for both a decent revenue and keeping the basic SprintTimer on a low, one-time charge.

This page is also available at sprinttimer.se/support