A Curiousity

This is a mile stone that used to be on the Midlands Hwy. On one side it has the distance to Launceston and on the other side it has, well, it doesn't have the distance to Hobart Town. That bit is blank. It's not an anomaly either. There's a bunch of them now at Clarendon, and every one is blank on the HT side.

Of course, the question is why?