Connect the SWR meter to the rig aerial output and connect the twig to the SWR meter.

Select a channel. (Channel 20)

Switch SWR meter to Forward.

Key mic and adjust SWR meter to give Full Scale Deflection.

Release mic and switch SWR to Reflected Power and key mic again.

Read the meter.

Repeat for channels 1 and 40.

All Reflected Power readings should be below about 1.5.

If any or all readings are above about 1.5 then the aerial length or ground plane size need to be adjusted. In general it is impractical to alter the size of the ground plane (you could go and buy a bigger or smaller car) so the twig will need to be lengthened or shortened until the SWR is the lowest possible. The lengthening or shortening can be measured in just a few milimetres and can be achieved by lifting or lowering the whip in its base. It isn't recommended to cut the whip until you are aboslutely sure because you cannot put back what you have removed. If in doubt live with a slightly high SWR. After all the difference in power output of a SWR of 0.1 and 1.5 can be measured in milliwatts and will make no practical difference to distance except in the most extreme circumstances.

Don't forget to disconnect SWR meter and re-connect twig direct to rig upon completion.

Alternatively it was possible to buy a SWR meter which incorporated an Aerial Tuning Unit. This device does away with the need to alter the twig size as the matching of rig to twig is done electronically. This device remains connected during use. With an ATU it was possible to obtain a SWR of zero for every channel by making minor adjustments whilst transmitting normally. It was particularly useful if the breaker was using a Kicker, as at higher power outputs the SWR becomes increasingly important. With a Kicker a SWR of even 1.5 was considered to be pushing it.