This is not related to the troll yard art except that it is
another calendar designed to be yard art. Here's an explanation
for how this device works. There are two gears connected by a
chain. The bottom gear has 9 teeth. Additionally, it has 14
wires with hooks on the end. A plant hangs on the bottom
hook. Each day, the plant is moved to the next hook so that
the chain moves in a clockwise direction.

The chain drives the upper gear clockwise. The upper gear has
19 teeth. The chain has 235 segments. Additionally, the upper
gear has 19 holes, one to a tooth, constructed to hold two
pegs, a short one and a long one. There is a mark on the chain
indicating the start of a new year. Each time that mark lines
up with the short peg, the long peg is moved one hole counter-
clockwise. If the short peg is in the spot, it is moved to the
hole previously occupied by the long peg.

A new year starts each time the marked segment on the chain
arrives at the same spot. A new lunation starts each time the
small peg on the gear arrives at the same spot.

The daily manipulation is accurate to one day in just over 3
years. This error can be corrected by moving the device if
needed when there is an eclipse. I suggest using lunar
eclipses since they are more common and easier to see.