Topband: Measure DOG to calculate BOG

[Mikek]

I once saw a print up of laying out a Dipole on Ground and doing 
measurements
and adjusting length and then using that to figure out a proper length 
for a BOG.
Does anyone know where It.
   Can you explain why that is an advantage over laying out a BOG and 
measuring it directly.

                              Mikek KF4ITA