I have one of those Duplex Meggers too, Dave, kindly donated to me by my good friend and fellow Forum member Jim Medley. Mine has push-in terminals and works well, apart from the movement having a tendency to stick at the LH end. A gentle tap on the case before winding the handle always frees it off. I think that these were designed for electricians testing electrical installations for compliance with the then IEE Regulations, perhaps the edition from around 1937 which called for an insulation resistance > 1 Megohm and an earth continuity of < 1 ohm. Pity the low resistance range isn't properly divided up and scaled. Mine lives in my tool box and gets a regular outing once a month at the Repair Cafe.
I absolutely agree, Trevor. These small Meggers are positively beautifully built inside, and the Bakelite case is so thick and solid that it looks like it should survive a hammer attack, or at least a severe drop test. That said, we have a 500 volt Wee Megger at the Black Country Museum with a bosted case. Oh yes, I've got an Avo light meter too, which I actively use for measuring the candlepower output of vintage paraffin lamps... but I digress.
Going back to the Circuit Testing Ohmmeter, it appears that there were four versions made, with different scale ranges, of which I now have two, and a growing desire to obtain examples of the other two, which I'm trying hard to resist
It's the 0-3 ohm range that is proving the most useful, as this covers the very low regions of resistance that most conventional Avometers struggle to reach.