Although many of the older GH members know about this procedure, many of you younger folks probably have never worked with an old fashioned "point type" distributor. Here is how the old timers used to test the "point pressure" on a distributor lobe.
We all know that the dwell angle is the most basic setting on "point" actuated distributors, but those points had many weaknesses. Even though they may not have been pitted after 3000-5000 miles (the recommended change interval), many times the point spring was causing ignition problems such a "misses" and "backfires".
One of the most crucial items for this diagnostic was a distributor tester AND a "Point Spring Tension Gauge"
Look at this vintage Chrysler "Solar Spark Ignition" distributor form the ealry 1950's
The points tested OK with dwell, resistance and RPM on my Distributor Tester, so the last test requires a spring pressure test. This is where the gauge comes in.
The point rubbing block is positioned in the middle of a flat section of the distributor lobe. This assures that the points are totally closed. The gauge then hooks to the point tension arm and is pulled until the points just start to open -- at that point a reading in ounces is taken from the gauge. In our case it's 24oz.
Next the proper car model and year are scrolled and found on the Distributor Tester and the "Spring Tension" reading is noted -- in this case the reading is 17-20oz.
This variation (24oz vs. the OEM recommended 17-20oz) tells us that the tension is too high and that the new point set will most likely wear prematurely and may cause ignition problems quite early because the wooden rubbing block is pushing too hard on the distributor shaft lobes. The remedy is to realign the points, readjust the springs, or subsitute another set. In any case -- the Spring Tension gauge was an invaluable tool for bench testing distributors of the time.