Jed, I have been using manual tuners easily and accureately for 25 years.
The trick is a friend built me a voltage control oscellator.  It taps
across the watt meter, and as the voltage changes, the pitch changes.  I
can tune more accureately than a sighted person with this thing.  We've
compared to see.
Now I don't have a diagram, it was in a 1972 btp or qst, have no idea now.
You might do it with a neon bulb, a photo cell, and an oscellator, or many
other ways.  I know people have tried it with ic chips, but it is hard not
to get them to react with rf inside the tuner.
I drilled a hole in an old tuner, put a 1/4 inch head phone jack in it, and
put it in the bypass position so I only use the watt meter and the
oscellator out of that box.
The tuning here is done by the big mfj 3000 watt job, because the 600 wats
pep out of the valiant are to much for the origional tuner.
Howard