This reminds me of how we measured it back in high school...
It involved a battery operated bell and a huge long strip (as long as the drop from the window to the ground) of carbon paper with a weight on the end. Then dropped the weight while the bell was ringing, with the strip between the bell and the ringer lever thingy. The impact of the ringer made marks on the carbon paper, and of course the marks got further apart as the weight accelerated.
Measured the time it took to drop from the science lab window to the ground. Counted the total number of marks. That gave the number of marks per second or seconds per mark.
Measured the (varying) distance between marks. That, with the now known time between marks, gave the (varying) velocity at any instant.
And hence the acceleration....
But using a pendulum is by far the easiest way to do it... (As long as the bob is very heavy compared to the string, the whole mass may be deemed to be at the bob's CoG.) Beauty of the pendulum method is that since the period T is constant regardless of how wide the swing is, it can as suggested above be measured over 100s of swings and that reduces the impact of the reaction time when the stop watch is started and stopped.