Etymology of the word
The word whirligig derives from two middle English words: "whirlen" (to whirl) and "gigg" (top), or literally "to whirl a top". The Oxford English Dictionary cites the Promptorium parvulorum (ca. 1440), the first English-Latin dictionary, which contains the definition "Whyrlegyge, chyldys game, Latin: giracu-lum. It is therefore likely the 1440 version of whirligig referred to a spinning toy or toys.
Origins and evolution
The actual origin of whirligigs is unknown. Both farmers and sailors use weathervanes on an ongoing basis and the assumption is one or both groups are likely the originators. By 400 BC the bamboo-copter or dragon butterfly, a helicopter-like rotor launched by rolling a stick had been invented in China. Wind driven whirligigs were technically possible by 700 AD when the Sasanian Empire began using windmills to lift water for irrigation. The weathervane which dates to the Sumerians in 1600-1800 BC, is the second component of wind driven whirligigs.
Nice simple projection using the following:
At the posted coords count the Number of Whirligigs (NoW) you can see along the fenceline and multiply that number by 10 to find X.
NoW x 10 = X
The offset is X metres.
X + 115° - Bearing of Final (BoF)
Final is X metres.
At a bearing of BoF°