In an experiment I hope to carry out, one of my "constants" are velocity (constant velocity). I must say a way I will keep this value constant. For example I can not say "I will try my best to pull mass at a constant velocity" "I will take a video of the experiment. When I examine the video, I will measure the time for the reference point on the block to pass the markings. This data will be included in the report. I will consider the velocity to be constant if the time to travel through equally spaced markings is within + or – 5% of each other"