getting incorrect Voltage readings? The reasons.

A few additional things you need to be aware of:
  Look at the service data. In early sets often the meters were 1L ohms per volt. Your new fangled digital meter with many megs per volt will not load the circuit like the "old Timey" ones did.
 Many measurements later on were with 20K ohms per volt meters, BD (Before Digital).

Line voltages on early equipment were 110VAC Often they are from 120-130VAC. This will really skew your readings. A good reason to use a variable transformer connected to an isolation transformer.

READ THE NOTES ON THE SCHEMATIC! Often they state the voltages can be +/- 20%.

 Now add that to the higher line voltages these days and you can really chase your tail all over trying to find a non-existent fault.

Remember, when doing voltage measurements, take into consideration the voltage standards were made with specific meters at that of time of manufacturing. Not as accurate on the bench unless you were using Calibrated Standards.

This video shows the difference of two DVMs that are highly accurate, but yet not the same. Why?