How universal is the flapper size? Do I need to measure the existing one before buying a replacement?

Awesome comment! Yes, this YouTube video is excellent.

In light of your comment, I re-evaluated my own process, and realized that there is absolutely no need to disassemble the sandwich. I've completely revised the guide. So... your comment no longer makes sense, but digital archaeologists will know that your comment used to make sense, and in fact guided me to an overhaul of this guide. Thanks!

Wow, that sounds delightful. Is there any chance that your procedure would apply to the watch in my pictures as well?

Oh! Interesting! I should update the instructions to reflect that.

Oh! golly, is that necessary? I’m trying to remember whether I did that. Okay, explanation, apologies if you already knew all of this.

1) The term “short” refers to creating an electrical connection, sometimes known as a “short-circuit”, between two points.

2) The term “pads” refers to electrical contacts.

On the sticker (in the photo above), you will see an arrow (really more of a small triangle) at the lower right of the sticker, pointing to two circular metal contacts, or “pads”. In order to reset the watch, I believe you will need to create a “short” by touching both of these pads with a conductive object. A short piece of copper wire would work, or nearly anything else that’s conductive. Let me see… Actually, if you took any unplugged appliance, you could probably use one of the prongs of a 110VAC plug to bridge these. (Reiterating: NOT WHILE IT’S PLUGGED IN.) Maybe it would be safer to use a fork, spoon, or conductive screwdriver.

I’m guessing that I did this, and neglected to mention it. Yikes!