Welcome to another postcode cache situated just off Highway 8. This cache will count as a find in Tatiara, the good country. This is a two stage multi with a very short drive between the listed coordinates and the final. It slightly favours Bordertown/Melbourne bound traffic, but not a big diversion for Adelaide or Naracoorte bound traffic.
Wikipedia tells me that the town was named after the home town (in Scotland) of Lord Kintore, who was the governor of South Australia at the time. The post office opened in 1874 as Mount Monster, and was renamed Keith in 1904. I kinda like Mount Monster.
At the listed coordinates you are standing in front of the present day post office. Turn to the bank of post boxes to find the numbers to guide you to the cache.
Let ABC be the digits of the number of the box to the right of #285
Let DF be the digits of the number of the box to the right of #78
The cache can be found at: S 36º 06.(F - C)(A x 2)D E 140º 21.(A + C)(C x 2)D
Checksum of the minute decimals is 42.
I hope you enjoy your stop in Keith, be sure to have a ride on the coaster, and have a safe onward journey.