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I built one of those MM-1s about 50 years ago. Mine said "5000 OHMS/VOLT AC 20000 OHMS/VOLT DC". Note the slash (/) in there; it means "per".

Using that and the range/function switches will give you an idea of the "impedance", although that would probably not be very useful for precision work. I doubt whether "setting the RX", whatever that is, qualifies as "precision".

Impedance is an AC term which involves resistance along with inductive and capacitive reactance. If we knew what you're trying to do with the meter we might be able to help more.

Edit: http://www.heathkit-museum.com/test/hvmmm-1.shtml
Here's an old picture which you've seen if you've been Googling. Note that Heath correctly calls the 5000 ohms/volt AC and 20,000 ohms/volt DC "sensitivity" rather than "impedance". Sensitivity is a measure of how much voltage must be applied to give precisely a full-scale reading. It's so much less sensitive on AC because the AC signal, of whatever frequency (!) has to be rectified and filtered before it can be applied to the meter movement. Lots more circuitry involved; lots more places for something to go rwong.

<blockquote data-quote="Beetle" data-source="post: 423743" data-attributes="member: 1066">I built one of those MM-1s about 50 years ago. Mine said &quot;5000 OHMS/VOLT AC 20000 OHMS/VOLT DC&quot;. Note the slash (/) in there; it means &quot;per&quot;.&nbsp;Using that and the range/function switches will give you an idea of the &quot;impedance&quot;, although that would probably not be very useful for precision work. I doubt whether &quot;setting the RX&quot;, whatever that is, qualifies as &quot;precision&quot;.&nbsp;Impedance is an AC term which involves resistance along with inductive and capacitive reactance. If we knew what you&#039;re trying to do with the meter we might be able to help more.&nbsp;Edit:&nbsp; <a href="http://www.heathkit-museum.com/test/hvmmm-1.shtml" target="_blank">http://www.heathkit-museum.com/test/hvmmm-1.shtml</a>Here&#039;s an old picture which you&#039;ve seen if you&#039;ve been Googling.&nbsp; Note that Heath correctly calls the 5000 ohms/volt AC and 20,000 ohms/volt DC &quot;sensitivity&quot; rather than &quot;impedance&quot;.&nbsp; Sensitivity is a measure of how much voltage must be applied to give precisely a full-scale reading.&nbsp; It&#039;s so much less sensitive on AC because the AC signal, of whatever frequency (!) has to be rectified and filtered before it can be applied to the meter movement.&nbsp; Lots more circuitry involved; lots more places for something to go rwong.</blockquote>

[QUOTE="Beetle, post: 423743, member: 1066"] I built one of those MM-1s about 50 years ago. Mine said "5000 OHMS/VOLT AC 20000 OHMS/VOLT DC". Note the slash (/) in there; it means "per". Using that and the range/function switches will give you an idea of the "impedance", although that would probably not be very useful for precision work. I doubt whether "setting the RX", whatever that is, qualifies as "precision". Impedance is an AC term which involves resistance along with inductive and capacitive reactance. If we knew what you're trying to do with the meter we might be able to help more. Edit: [URL]http://www.heathkit-museum.com/test/hvmmm-1.shtml[/URL] Here's an old picture which you've seen if you've been Googling. Note that Heath correctly calls the 5000 ohms/volt AC and 20,000 ohms/volt DC "sensitivity" rather than "impedance". Sensitivity is a measure of how much voltage must be applied to give precisely a full-scale reading. It's so much less sensitive on AC because the AC signal, of whatever frequency (!) has to be rectified and filtered before it can be applied to the meter movement. Lots more circuitry involved; lots more places for something to go rwong. [/QUOTE]

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