It's not a simple conversion because it's not a common conversion. It's like converting between inches and meters. The imperial system is multiple systems smashed together, and it's optimized for the more common conversions.
Not saying it's a perfect system, or that metric isn't better, but it's absolutely useable. I'd much rather stick with imperial than half-ass a conversion to metric and be stuck between the two systems, like what's happened in Canada and the UK.
who actually seriously uses decimeter on a weekly basis and what for?
I've used metric for 50+ years and I'm in the field of sensors and measurement with application from remote sensing to minerals and energy .. and I've yet to use a decimeter unit (outside of a programming exercise).
The convential usage is pico, nano, milli, centi, and full metre (and upwards to kilo, etc).
I mean, who uses feet anymore anyway?
I've just measured up a whole bunch of stuff making a parrot proof covering for a pear tree .. everything is jotted on the back side of a bit of board in mm (millimeters).
3230 mm is 3.2 metres and a bit .. a bit under 10 & a half feet (but, again, who even uses feet or thinks in them anyway? *)
* We do use yards for conveying to USAians what distance we shoot targets at on the farm; (eg from the next door neighbours youtube channel [1] 5023 yards 24" x 24" target ULR shooting)
But doing things at yard scale in mm is not helping the cause. Who wants to be throwing around 4 digit numbers in their head?
Millimeter fit on cabinets is the fit you want, whether you work in metric, British Imperial, or US Common.
When you have a long kitchen counter you're looking at 3 metres or more ( ~10 ft ) with framing and doors that join with barely the width a fingernail between.
The measurements are 10 foot (two digits), 6 inches, (another digit) and then a bit (tenths or hundredths of an inch, or a fraction - depending which you prefer).
That's ~ 4 digits for each measurement on a common household task.
It's pretty simple doing this as 3245mm on paper .. tradies have been doing this here since the 1970s and nothing's fallen down yet.
Dunno about you, I'm primarily a mathematican doing applied work - but I've worked as a TA (trades assistent) in electrical, gas fitting, plumbing, heavy mechanical, rigging (multi sling heavy lifting), welding, etc. (too much exposure to minesites and cattle stations I guess) and there's an entire class of people that are comfortable working with measurements that span the length of a truck and are accurate to the millimetre (or tenth of an inch) - so, four digits? No worries.
Why do you struggle with that?
You are doing precision work while I'm picturing loosy goosy mental estimations.
Now I am curious as to why not. is it just in that spot where no one really needs a measurement? in the US we went the other way, the yard(the long human scale measurement) is almost never used and the foot(the short human scale measurement is much more common.while in metric land the meter(the yard equivalent) is much more common and the decimeter(the foot equivalent) is never used.