This is an IR (infrared) sensor based digital stop clock. Two sensor pairs are used; one of
these is fixed on to the upper clamp holding the tube and second pair is fitted on to the lower
clamp holding the tube. When the sphere passes across the upper sensor, the clock is reset (to
00.00) and it passes through the lower sensor it halts the clock (i.e. the clock stops counting
time). In this manner the time taken by the sphere to travel from the first sensor to the second