There will be better UI when the webui is rewritten.
You can turn on the PID debug by doing a "set" command to set tp to 1. The easiest way to do this is on the bottom of the configuration page, there is a "Raw set command", just enter tp=1
TP is short for "temporary parameter" in that it isn't stored in eeprom. The first value happens to enable PID debug. You can also turn it on on your desktop browser and it stays on until reboot across all clients.