$ units
Currency exchange rates from FloatRates (USD base) on 2020-05-12
$ sudo units_cur
$ units
Currency exchange rates from FloatRates (USD base) on 2020-07-09
Looking at the source of the default configuration (cat /usr/share/misc/units.lib), I believe it only defines conversions for currencies that are pegged to another one (mainly to EUR or USD).
You have: 10 franc
You want: dollar
conformability error
1.5244902 euro
1 usdollar
You have: 10 franc
You want: euro
* 1.5244902
/ 0.655957
I didn’t look too deep into it, my understanding was that the source it uses to update itself has been taken offline. There are workarounds involving data massaging and a cron but honestly that’s a lot more work than typing “1000 chf to usd” into ddg and getting the converted amount. But if you know something I don’t, maybe you could share for everyone’s benefit?