Totally agree. And how does it work when you measure a thing and it is 1,35 inch do you in the US convert it to fractions? And how then do you find this fraction?

A ruler sold in the US (and Britain, on the reverse/bottom) has inch markings with fractions.

│.╷.|.╷.│.╷.|.╷.│.╷.|.╷.│.╷.|.╷.│

0⅛¼⅜½⅝¾⅞1

So the measurement, when taken, is 1⅜".

I've seen inch rulers with different fractions, e.g. one end might be eights, the other sixteenths, turn it over and there are tenths.

(I don't know how this works with digital measuring devices — I grew up in Britain so have never used inches professionally. Only in Warhammer and TV screens.)

With digital devices I assume there is a mode switch like in the digital scales I have at home in the US. I actually work in grams for things like bread making which seems easier than a combination of pounds and ounces.

I think I want my writing to reflect how I talk or think about it. So if the spoken sentence is "specification is a half millimetre" then write with ½ instead of "0.5" because the former will be read out correctly.

But that’s my point! The way you talk or think about it is absolutely influenced by what you’re used to, and what you’ve grown up with.

To you, it’s obvious and natural that „half” is 1/2.

To me, it looks off and I have to „convert” it in my mind to 0.5, which is the way I think about it.

Exactly this. A “half” in my mind translates to 0.5. I don’t do any conversion, 0.5 exists as the very concept of “half” in my brain.