It sits between the lower standoffs to help maintain the position when winding. It is completely optional.
I added it after the initial release, but didn't want to change the assembly guide for this minor change. Editing the pdf file removes the old version from the zip file and doesn't always add the new one back in.
Well all I did to your original base.stl was to take a hollow tub in Tinkercad
down through the hole of the circle to just make the circle big enough for the slightly larger plastic coil cap. And into the body of the base to allow perfect fit of the little PCB. And just made the lower half of the pendulum arm end smaller.
It sits between the lower standoffs to help maintain the position when winding. It is completely optional.
I added it after the initial release, but didn't want to change the assembly guide for this minor change. Editing the pdf file removes the old version from the zip file and doesn't always add the new one back in.