The plunge routers I have used have an adjustment knob on a threaded shaft. All threads are based on a pitch. The proper pitch gauge (metric/imperial) will tell you what you have. If, for example, your shaft was 10mm x 1.0mm pitch then every full turn of the adjustment knob would equal 1 mm of height adjustment.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.