<VV> Timing Gun to plug No. 6

[Secular]

  Hi:

  Could the timing be adjusted [correctly] by attaching the timing gun to 
  another plug-wire other than No. 1 ? 

  I know....I know -- when setting the dynamic timing on a car, the engine 
  must be running at a set rpm, and the _first_ spark plug must fire when 
  the crank is at a specific angle before top dead center.

  But, how far off would the timing be if you're aiming for let's say, 18-BTDC 
  and the inductive timing gun is clipped to plug Number 6 instead of No. 1 ? 

  Regards,


  Tony