Click click click - oh pardon me I was having fun clicking away on my mechanical decade counters. Each order comes with five individual counters. They're snap together so you can connect as many or as few as you'd like. Each one has two buttons - an up counter and down counter. Once you get to 9 it circles back to zero. On the back is a PCB with 11 contacts - one common and then 10 that are shorted to the common one by one as the counter goes by that number.

These make for an interesting interface! This one is the smaller size with a bezel size of 1.85" x 0.94" (for 5 counters with 2 end caps)