First of all: thanks for a great app! I use it pretty much daily and really like it.

I have a few ideas about improvements though. First of all, the pressure unit kilopascal seems to be missing which is a bit funny considering kilo one of the more used prefixes for Pascal.

Millibar (mbar) and micron are two other pressure units that would be nice to include. Micron is a dumb unit but it's used for example in the US HVAC trade. See:
https://hvacrschool.com/what-is-a-micron/

Lastly, to avoid clutter, having prefixes separate from units could maybe be a solution. The list of units could be kept as it is but all variants of each unit is removed and a prefix drop down-menu is added where you can select your preferred prefix.

Again: Thanks for a useful tool!