- I think the unit of the Power Level is Ki. I would like to give you the link to the wiki:
The Power Level (戦闘力, Sentō Ryoku; literally "combat power" or "fighting strength"), referred to as Battle Point/Battle Power (BP) in video games, is a concept found in the Dragon Ball franchise created by Akira Toriyama. It is first introduced in Dragon Ball, where Goku as a kid learns to sense ki after drinking the Ultra Divine Water, although the Z Fighters are able to detect power levels via the ki sensing ability eventually.
It's not clear how they measure the power, or at least I couldn't find something...
That's right, Bulma got one of the scouters, so I think it shouldn't be a problem for her to copy it.
And if you want to know which character has which Power Level, see this list of Power Levels.