What is the unit of power level in the Dragon Ball series and how is it measured?
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.