How many monitor 121.5?

In article ,
Ron Natalie wrote:

Brad wrote:
.Blueskies. wrote:
The Maydays post got me wondering. I don't monitor except during the long
flights, maybe ~2 hours or longer...

Flying traffic reporters deep in the FRZ around the DC Beltway, I'm
always on an ATC frequency and monitoring air-to-air on the #2. If I
had a third comm...

Actually the SL30 (and the GNS480 which uses the same comm section)
can monitor the standby frequency. I can listen to 4 frequencies.
Even when I'm picking up the ATIS or something on #2, I've got 121.5
in the M channel.

It's mind boggling that it took avionics companies so long to add this
feature to their products. Dual watch was a standard feature in marine VHF
radios 15 or 20 years ago. I used to have an ICOM marine handheld that had
tri-watch. You could monitor two random channels, *plus* channel 16 (the
marine version of 121.5).