Gravel Road Tour series.
Note. 3 June 2021 formula has been updated since the cache was first published.
At the posted look for a township road sign (white characters on green background). Consider only the sides facing the roads (Panmure and Ridge). There are 3 address numbers. Arrange the 3 sets of numbers from lowest to highest and obtain an 11 digit number string and call this string ABCDEFGHJKL
Subtract L G-A D+H from the North posted and subtract G/D J-E+L K from the West posted to obtain the final coordinates.
The cache is about 3 meters from the ground.
While at the final coordinates check out the nearby grykes!.