This was created as part of Hackclub Construct.

A mechanical counter that counts from 0-99 on 2 wheels. It features a push button that increases the counter by 1 for every full push. It is fully 3D printable and there are no external components needed (although you can use a small elastic rubber band on the push button to make it come back up by itself).
The 2 arrows indicate the active number. You should read the number from left to right, with the bottom side of the contraption being the side with the push button.

To reset the counter I'd recommend taking the wheels off, putting the gears in their 0 0 position and placing the wheels back, or just moving the button out of the way and manually spinning the gears. (You can also just press the button 100 times to get it back to 0)

ASSEMBLY INSTRUCTIONS

DISCLAIMER: Use the 3D model for reference, it will help a ton.

Take the bottom case (the one with the shafts) and place it upright on your workbench. Start off by placing the spacers on the 2 largest shafts, with the short spacer on the inner shaft and the long spacer on the outer shaft.
You can now take the first gear (the one with 2 connectors coming out of it straight up) and place it on the inner shaft with the connectors facing up, and then lock the gear into place using the longer stopper (the longer L shaped piece with a whole at the end) by placing it on the shaft with an indent. Now, before placing the second gear, make sure that you position both gears in this exactly position.

Once you have them in this position you should lock the second gear in position by placing the second stopper, and once both are locked you can place the button (the longest L shaped piece) in position, but make sure that the shorter rod is inside the bottom case's channel (the one you are assembling now).

You can now place the top case into place and finish the assembly process by adding the 2 wheels on their respective gears while making sure that both of them have the 0 on the top case's arrows.

Thanks.