The reason is that it is a very big numner for these conversions:
1 EUR = 24810.7356 STD
The inverse obtained is obviously too small:
1 STD = 0.000040305133073120169802623667474011 EUR
This is more than the 4 digits after the decimal place.
Hence Google needs to increase the number of decimal places for such evaluations.
Doing it in FA with the default values will be of no use and hence @notrinos solution is elegant.
If you search for "1 STD = ? EUR" you will get 0.000040 as the answer now.
Hence their evaluator for the search engine is okay.
Incidentally, we may have a Chart of Accounts for Sao Tome among the forum users - @odaio!
Alternatively, if all the reverse rates work, then we can swap the currencies and make just 1 single check. The reverse for IDR to OMR does not work.
USD to any currency works - hence only when a non USD is involved as the From and To currencies, we will need 2 conversions and then a division! Here we will have the second check only when the first fails.