The WeberVST bias probe is a nice product. However, as Lance's instructions illustrate, users do run the risk of oversimplifying the process.
#1
You really should not be biasing your amp without knowing the plate voltage. The reason is that you need to be concerned about the power dissipated by the plates which is directly determined by the voltage on the plates and the bias current (Power = Voltage * Current).
Depending on your amp's plate voltages, your tubes could be running overbiased, underbiased, or perfectly fine at 35mA
#2
There is no magic bias current setting. The correct setting depends on the type of tube, the plate voltage on your particular amp (do NOT use the values on the schematic b/c they vary from amp to amp and even region to region depending on the exact voltage at your electrical outlet). The 35mA, 70% of max dissipation, roll a die and add it to 30, etc. methods all ignore the most critical issue, the player. You'll get a lot of opinions on what the bias current should be set at but this IMO is the best rule to follow:
The bias current should be set to the point that sounds best to YOU that is within the dissipation specs of the tubes
Hence, 35mA may sound good to you but someone else may like to run their tubes hotter. There is a trade-off here, colder biased tubes (less mA) will tend to sound more sterile, but they also last a lot longer. Hotter biased tubes (more mA) tend to sound warmer (up to a point), but their life can be significantly shorter (even seconds if you're over the plate dissipation of your tubes).
#3
After you set your bias, make sure you turn out the lights and have a close look at the plates of the tubes (the big, darkly colored flat element in the tube; not a good description I admit). If it's glowing RED you need to decrease the bias current, no matter what your math (Power = Voltage * Current) tells you.
Tubes vary and you probably have a set that don't quite meet spec. :)
Lance's method isn't wrong; it's just only half the story.