Planning to buy a Mallory distributor. Thinking I might need an "advance" timing light. Problem is I really don't know what they do or how they work. I have a basic strobe timing light. What does the advance feature do? Santa will thank those who can educate me.

The advance light lets you move around where the strobe light
appears to your eye.
For example, if you have a mark at TDC you can set your advance
on your stobe light to 10 degrees advance and when your
distributor advances to 10 degrees you will see the TDC mark.

The value is you can get pretty accurate readings with a single mark.
(very useful when using the standard 914 impeller which
doesn't have full markings)
If your mark is at 5 degrees BTC rather than TDC, then you would
add 5 to the setting on your light. ie, if you set your gun to
10 degees and the mark is at 5 then you have a total of 15 degrees.

I have one and I love it
Mine also will measure RPMs, Dwell, and even voltage.

--- bill

When I set up my Mallory I needed an advance timing light to make sure I was getting the advance I wanted. I made sure I could see the tdc mark on the flywheel, I was lucky it was marked with paint. I also set up the mallory where I thought would work for my engine. I figured that I could reset the stop inside the distributor so the advance inside would only be 8 degrees. Then I installed the distributor with the rotor pointing to the number one plug. I set up the timing light to get ready to set the timing. I fired up the car but it tried to kick back so too advanced I moved the mallory back then it fired up. I checked the total advance at 3500 with out the vacuum hose connected. With my non advance timing light I set the full advance just past the 27 degree then drove it to my friends shop for the final setting. I found with the advance light I could dial to the 12 degree and check to see if tdc mark matched up. It matched up with the 10 degree so I advanced the Mallory so I would be at 11-12 degrees at idle say 900 to 1000 rpm. Then I reved up the motor to 3500 and matched up the dial with the tdc mark it was at 31 a little more then I wanted so I took the Mallory off and loosend and moved the stop inside it lessen the max advance. I reinstaled the dizzy set the initial at 11-12 then checked the total and it at 29 where I wanted it. With the advance light I could see the timming at 1000, 1500, 2000, 2500, 2900 I think was after full advance, I charted the grey, grey springs I just have to find it. I car run great. No more pre-ignition or detonation from the CA. gas . The 009 sucked on my 2.5l motor. Sorry about the length I was getting all of my thoughts collected . If you get the advance light you can try different setting to see what works best. I think 11 to 28 is best for most type 4 motors. I have learned that most people set the springs so that the advance does not start until 100 rpm higher then Idle but I ran out of time. 11 idle @ 1000 , 12 @ 1100, 29@ 3000+ Thats what I have 18 degrees total advance I may be able to go to 16 degrees but it feels good where it is at now. I hooked up the vacuum then checked the max advance , then reset the set screw in the vacuum canister so it would stop at 34 degrees while running down the freeway. I increased the mileage by a couple miles to the gallon but I know to watch for detonation from too much advance. I hope this helps. 8 degrees in the mallory = 16 advance , 9 in mallory=18 advance, std setting in mallory is 12 inside 24 advance. I think that is right , oh well I have been wrong before. Thanks Mark