The Mk30/Mk29 combination of altimeters is used in both the Tucano and Canberra, albeit with one in each cockpit. As the report states, the Mk30 is a very accurate servo altimeter, but without 115vac it will freeze. The Mk29 when used in Reset will effectively mimic the Mk30, but will still allow a different pressure setting to be used if needed.
If the Mk29 is left in Standby then it ignores the electrical input from the Mk30 and becomes a normal (none-servo) altimeter. It does have a vibrator to help eliminate stiction. In the Canberra the Mk29 was the main altimeter for the pilot (the nav had the Mk30) and was often used in standby mode. Although not quite as 'smooth' as the Mk29 it was perfectly useable for aeros. Spent many aeros sequences in the back of a Tucano watching the Mk29 in either mode and it was perfectly good in either!
Even if its wasn't covered in Hunter 'ground school', I'm just amazed that AH didn't wonder what the R/S knob on the LH Mk29 altimeter did in the Hunter. I simply can't comprehend any pilot (therefore naturally inquisitive) not wanting to know.