Is this a Warco / Metric thing...or am I just out of date?

My mini lathe has an indicator in mm. So to adjust the diameter, you have to divide the difference in measured and requested diameter in 2. Not a real problem but still a source for error.

My bigger lathe has a dial in Ø, that is easier to use and is my preferred dial. Luckily making a dial is not so complicated so a custom dial can be made.

If using an unfamiliar tool then checking these things is essential before cutting metal. It is not always obvious if a machine is metric or imperial so make some checks. The cross slide being calibrated for diameter or radius is a classic area of confusion, I would hesitate to attribute the convention to an Atlantic divide as British machines are not consistently one way or the other.

Mike

My 1963 Colchester Chipmaster is graduated on diameter.

I also checked one of my old text books. "Basic Engineering Processes" by S Crawford, first pubished in 1964.
He was the manager of the technical training workshop at Rolls Royce Bristol. He notes on the description of the Cross Slide "The reduction in diameter will be twice the value of tool movement indicated by the graduations"

I also have my apprentice journal from 1980, I learned to turn on a Colchester Student 1800, no mention there of cross slide graduations and radius/diameter. I have to assume it was aslo showing diameter as wehn i got my Chipmaster at home some 30 years later, I didn't have any surprises.

So definitely not a new challenge

Something that just ocurred to me - tool movement would be preferable to diameter reduction if you were screwcutting and wanted a specific thread depth i.e. "working to the book".

I just keep cutting and testing until a nut goes on...

Rob