That was introduced early in Don Hooker's design career during the late 40s with the one balls. I'll have to go back and re-read some of my code to figure out the first one... The same feature carried over to the bingos (modified).

The one balls can step six steps(!) On a single coin.

key west had score extra step when it left the factory. You'll need to see if it's been disabled.

how frequently you got extra steps depends on the cam profile of the score extra step pulse generator unit on the mixer shaft.

for a bad explanation, see http://bingo.cdyn.com/techno/howtheywork/scorexstep/

I just noticed on my County Fair (working machine) and my Bikini (project) the extra stepping have been physically removed from those machines.... BUT I have a parts machine that the extra stepping is still present, just wondering what it takes to put into the County Fair/Bikini, Im kinda thinking it's more work than worth having that additional stepping for a Bingo noob....

the main parts are:
- extra step relay - usually mounted on top of the mixers
- extra step index unit
- extra step pulse generator assembly on the mixer shaft
- usually a square pin switch mounted under the pulse generator

the cam profile on the pulse generator may be different. The ones on the early machines had more/wider cam ledges, so extra steps were more likely. No harm to swap them around tho, you just get more/less extra stepping than originally designed.

if the pulse generator is missing, the easiest thing is probably remove the spotting slip ring wipers, spotting wipers and unscrew the spotting disc brackets from the back plate so it can be tipped off the shaft (if the wire harness has enough slack and you may need to unscrew search relays from back door), then you can slide the pieces onto the shaft after removing the spacer tube.