[resonator]

Dividing it by two gives you 3/8 rather than 9.5mm. Dividing it by 4 gives you 3/16 rather than 4.75mm. Both 3/8 and 3/16 are common sizes. You can drill holes cut grooves this size. You can use your 3/8 chisel to quickly find the centerline.

It's not like you can't do any of this with the metric system, but you'll either need to measure things more, or round things. Often rounding is fine, but to me it feels like a compromise that is born out of the measuring system; a compromise that isn't needed when using the imperial system.

[avmich]

It's like suddenly listening to an unfamiliar language.

"Dividing it by two gives you 3/8 rather than 9.5mm." - so? What's wrong with 9.5 mm? And what's going to happen when you divide by three, not two?

"It's not like you can't do any of this with the metric system, but you'll either need to measure things more, or round things." - won't you need to round things in any positional system when you divide in not a divider of the base of the system - that is, in imperial system the base is 2, and you have convenient halfs, quarters, eights... and in metric the base is 10 and it's convenient to divide by 2, 5 and all combinations of 2s and 5s - like 50 or even 125.

In your example, 3/4 is 0.75, and divided by 2 is 0.375, and for quick estimate for what it would be in inches you take an inch as 25 mm and go from it.

Don't see anything natural in one compared to the other.

[resonator]

> What's wrong with 9.5 mm?

As a number, well nothing. I'm not saying there are anything wrong with the numbers, I'm saying that with a standard set of imperial or metric tools, you're more likely to find your imperial tools working with with you.

> And what's going to happen when you divide by three, not two?

Well dividing by three will be 1/4". That's another common imperial size. But to answer the point I think you were trying to make, there are sometimes cases where it isn't natural — like dividing 3/4 by 5. In those cases you need to measure or pull out of divider. Your problems don't all disappear when using imperial but I find that more often the perfect dimension happens to be that of a commonly size tool.

> Don't see anything natural in one compared to the other.

I think you're arguing from the perspective of pure numbers verses the practicality of making something with tools that I own. If I was using CAD, it metric or imperial would make zero difference.

[moogly]

> with a standard set of imperial or metric tools, you're more likely to find your imperial tools working with with you

... when working with imperial, you mean? Or do you mean regardless if you target metric or imperial?

[resonator]

Actually, I take it back. As I said earlier, I mostly use vintage imperical hand tools. I've just been looking into modern metric tools and I'm finding that they're actually imperial, as in they come in sizes like 0.25"/3.2mm. So long as they're not rounding them to whole millimeters, they'll have the same ratio as the imperical tools.

I guess you can use whatever number system you care for.

Thank you for making me think about this.