If you don't have a 'scope you only have part of the picture.
Pun intended.
The shape of the modulation peaks is a big deal. They should be nice, sharp and pointy. The SSB limiter is meant to keep the drive level below the threshold where those peaks begin to flatten on the top. A RF wattmeter is subject to multiple compromises to its accuracy. Its accuracy on sideband can be limited by more than one factor.
Using a meter alone to set the limit in a sideband transmitter will work, so long as you're willing to be disappointed with the meter reading.
Peak meters were not so common 47 or 48 years ago, and interest in SSB above channel 23 (so-called "HF" operators) was getting large. I had a demo for the operators who thought an average wattmeter should show more on sideband. I would set the ALC for max wattage. The 'scope would show a horribly-flattened waveform, the monitor speaker would reveal distorted audio, and the Bird wattmeter would show 14 or more Watts. As I turned the ALC trimpot, there would be a threshold where the average wattmeter reading would take a nosedive, falling to half what it showed at full blast, the spiky audio-peak display would return on the 'scope screen and best of all, the raspy distortion in the monitor speaker would disappear.
Once they could see and hear what they were choosing, I left it up to the customer how he wanted it adjusted. Dern near all of them chose to sound better. It was a safe bet his wattmeter at home offered only an average reading, and this let me sidestep the annoyed call from a customer about "not enough wattage".
Sidebanders were a quirky bunch back in those days, and wouldn't talk to AM operators. Those days are long, long gone now.
73
