How are the yellow lines like? Is it like 2 vertical lines and your hands must be between them? Are they close together?
Both lines are 75 cm apart. Elbow at least 90 degrees bend with the back straight and arms fully extended to be considered a good push up.
The board (where you place your hands) will vibrate and the blue light (sensor at the front of the display panel) will blink if your push up meet the standard.
The machine will prompt you (when PU is not to the standard) by telling you either 'keep your back straight', 'chest go lower' or 'straighten your arms', so listen to the cue from the machine as why your PU is not valid/ counted/
Try to request for the 'trial tag' to try out the machine prior to your test in order to have a better understanding on how the machine works.