Hi Brenda:

While learning about the technical aspects of the LM 18 I discovered that they had a lot of very sophisticated temperature compensation. Pretty much every component related to frequency has design elements aimed at temperature stability.
https://prc68.com/I/USM159.html#LM_18_Frequency_Meter

I can think of a couple of reasons the on board frequency meter would be used:
1. If a new frequency was learned via a radio message, or
2. a plane landed at a facility were there was minimal ground support and the radioman needed to setup a new frequency list for a new mission.

-- 
Have Fun,

Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------

Date: Wed, 1 Oct 2025 17:53:11 -0400
From: Brenda Gentry <[email protected]>
To: [email protected]
Subject: Re: [Milsurplus] Aircraft use of freq meter
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

I have had the same question for some time. Would an operator need to 
change frequency that often in flight? If the practice was to "net" all 
of the transmitters before takeoff, wouldn't it be quicker to do it with 
an airfield reference?? How accurate would it be at 20 degrees below 
zero at 25,000 feet?

 ?? B.Gentry, KA2IVY