Electric choke

Here is what you are checking:

The circuit path for your ignition feed is

The battery -- fuse link -- through the bulkhead connector -- ignition switch connector -- through the switch -- back out the switch connector on the ignition "run" or "dark blue" -- back OUT the bulkhead connector -- to the ignition system, the alternator field, the regulator, and the electric choke if used

Every connection I mentioned, especially the bulkhead connector (twice) and the ignition switch connector (twice) can be a poor connection and lose a tiny (or large!!) amount of voltage when supplying the load (ignition system.) The switch contacts inside the switch can get "poor" and lose some.

If you have a "near perfect" circuit, there WILL NOT BE measurable voltage drop, and by "near perfect, I mean nice big wires, better connections everywhere, etc.

That's why you are talking in tenths of volts. MANY of these old cars are far worse. I've helped a few guys on here, and my own 67, before I fixed it, had ONE VOLT drop in this circuit.