Big numerals, 1/100 second
Giant numerals record well on videos of experiments.
The apple timer included with my iPhone does not let me make the numerals large enough to see from a distance.
The only app that shows to the full 1/100 second time position.
For example: With this timer running in the background of an experiment my class can slow-mo video record a falling pumpkin, use video edit mode to examine the fall frame by frame, and see the motion down to the 1/100 second.