If I have followed the thread properlty, you have a VSWR meter and you have
now decided to replace the coupler. The meter movement is actually intended
for another project.

It might not have occurred to you that if the diode voltage drop is small
wrt the RF voltage being rectified, that the 0 to 100 meter scale could be
taken to be rho (the magnitude of the complex reflection coefficient) in
percent. But, there is an if in there, verification is needed.

The calculator at http://www.vk1od.net/calc/tl/vswrc.php accepts rho as an
input (it is called the voltage reflection coefficient in the calculator).
So, if you were measuring SWR and you had 'set' the fwd direction for fsd,
then read for example 15/100 reflected, rho=0.15 and the calculator will
tell you that VSWR=1.35.

Owen