There are several clocks available for sale on Tindie, but one thing that they all (hopefully) have in common is that they keep track of time in a predictable manner. You expect a device that “ticks” once per second, that a minute is 60 seconds, and that an hour is 60 minutes. Of course some clocks may operate on a 24-hour schedule or even forgo the minute hand/digit, but other than that, things are pretty standard.
And then there is Nick Sayer’s Crazy Clock. This clock movement looks exactly like what you would find attached to most wall clocks with one major difference: it can be programmed to tick in a non-normal way. This can take several forms, including the Crazy clock, where it runs at fast, slow, or normal speed; Early clock, where it will always be between 0 and 10 minutes fast; the Vetinari clock (inspired, it would seek, by the book Discworld), which runs slightly slow, but adds a tick occasionally to make up for it; or many other options.
Additionally, it can be programmed to Martian time, or several other useful non-traditional options. You can also buy just the controller board and install it in your own clock movement; the video below should give you an idea of what is involved.
For a little more background on the clock’s creator, check out my seller interview with Sayer here!