This method requires more equipment than the direct comparison method, and
does not easily work on some electrical, mechanical, or electro-mechanical units.
It also does not test the functionality of the stopwatch or timer, only the time base.
Function tests need to be performed separately by starting the unit, letting it run
for a while (a few minutes to a few hours, depending on how the unit is used),
and stopping the unit. If the unit appears to be counting correctly, the displayed
time interval will be accurate.