Chevrolet: Ignition Timing Light vs Vacuum Gauge, vacuum gauge, deg btdc

Question
Roger,

I set the ignition timing on my 1966 Chevy using a timing light.  Plugged the vacuum advance, dwell at 30 deg and idle at 500 rpm then set the timing 4 deg BTDC.  I then hooked up my vacuum gauge which indicates late ignition timing (around 15 - 17)  Which reading is accurate, the timing light or vacuum gauge?  Any suggestions?  Am I going about this incorrectly?

Thanks  

Answer
Gerald;
      OK ,  you are timing it the right way and as far as the vacume gauge - at times the gauge will not read correct due to where you have it pluged in. As long as it is running right - the vacume gauge is prob. off  or not enough vacume from the spot were you are feeding it from .
I would not worry about  it. just have the idle set right so it will not stall on you. it can go up  more than 500 -  600-650 rpms  ok and with the idle higher the vacume should go up also.