A lot of antenna tuners have built in SWR meters and that is how they do it. If someone doesn't know the answers to the following questions, he will learn something important by figuring out the answers.
RIG -> SWR1 METER -> ANTENNA TUNER -> SWR2 METER -> coax -> ANTENNA
What does the SWR1 reading tell us? What does the SWR2 reading tell us? What if we replace the 50 ohm coax with 450 ohm ladder-line?
What if it goes: TX -> METER -> TUNER/METER -> ANTENNA
I have this setup (the first meter is more sensitive than the second) and occasionally the results differ. USUALLY they are in sync, one goes down the other goes down, but sometimes they act in see-saw fashion! You can't make one go down w/o raising the other one.
Is this because one meter is riding on a "trough" and the other is riding on a "peak" of the standing wave? Or is this another way of saying I have a "magic length" coax that is just the right size to invert the wave?