I use a protractor or square whenever setting angles and a quick guide can be made via protractor and sliding bevel, then create a constant guide in timber or ply.

Grind angle guides can typically be found stamped/engraved on the cap iron/chip breaker on most bevel up planes. 🙂  Muscle memory soon kicks in with practise, but – while there’s no real need for engineering accuracy – there’s absolutely nothing wrong with periodically checking for ball park accuracy.  One person’s ideal honing/whetting angle can be another’s pet hate and visa versa. 🙂

Rough guides

Paring = 20 – 25 deg

Grind = 25 – 30 deg

Hone = 25 – 35 deg

A pretty broad range of angles with overlap between grind and honing/whetting angles.  All depend on materials, tool type and the work to which any given tool is being applied.  😉