Found an old 500d. Has a good dummy load so worth keeping. I tried to use it just for fun to test SWR. Instruction sheet says for SWR it should first be calibrated to the 'SET' mark on the SWR scale while in the FWD mode. However, there is no 'SET' mark on that scale. Does anyone know if one of the numbers on the scale is perhaps the 'SET' mark? Thanks.