G'day, I have a list of readings for the different coins and I realised that I don't have a number for an older round 50 cent coin. I have never found one. I set my meter to read 150 on a 1 dollar coin so that a new fifty cent reads 144. I am presuming that with the higher silver content of the coin the reading should be at least 150 or above but that is just a guess, regards Neil