A suggestion for your speed converter: different sports use different units which your converter could support as well.

A few examples:

Running usually measures pace in minutes per kilometer or mile. That will be extra fun for you since it wouldn't be 4.33333 min/km but would be written as sth like 4:20 min/km.

Swimming uses min/100m or sec/100m.

Rowing uses min/500m.

If you add these then I'd be using this a lot!