Timing methodology · current review
How we’re checking lap timing accuracy
We compare the app’s lap registrations with frame-by-frame video of the car crossing the finish line.
Watch the video example
See Backyard Lap Timer in action.
01
Record a reference pass
Review footage recorded at 240 frames per second. The center of the front wheel is followed as a consistent visual point on the car.
02
Mark the registered crossing
Frames immediately before and after the app registers a lap are compared with the frame where the car appears to cross the physical finish line.
03
Estimate the physical line
A wooden board in the scene is used as a visual reference for the line marked in the app. It helps locate the crossing, but the camera is not perfectly aligned with the phone, so perspective adds uncertainty.
What this review can tell us
At 240 fps, consecutive video frames are nominally about 4.17 milliseconds apart. Frame-by-frame review helps locate a crossing within the recorded sequence and compare it with the app’s registration.
That 4.17 ms interval describes the video’s frame spacing; it does not prove the app is accurate to 4.17 ms. The current images also do not establish a validated distribution of lap-time error or a precise end-to-end processing delay. Camera alignment and the estimated finish-line position remain sources of uncertainty.
Preliminary findings
What the test shows so far
- Reference footage: the source recording is 240 fps and was slowed to 25% in a 60 fps edit. That gives a nominal 4.17 ms interval between source frames.
- Example app reading: one captured screen shows lap 9 of 10, total time 1:18.733, a best lap of 6.617 s and a last lap of 8.317 s. These are the timer’s displayed values; they have not yet been verified against synchronized reference timestamps.
- Crossing review: the images mark the front-wheel center around app registration and use a wooden board to estimate the physical finish line. Camera alignment adds uncertainty to the exact crossing position.
These findings are provisional. No numerical lap-time error or per-crossing processing delay has been validated yet; more controlled tests and paired timing data are needed.
Want to help test?
If you’d like to participate or send reference footage and lap data, please email backyardlaptimer@gmail.com.
Visual evidence
Images from the accuracy review
This sequence includes marked frames around lap registration and images used to estimate where the car crossed the finish line. Select any image to view it full size.
