Arduino nixie v41 Operating Instructions Manual page 8

"18" HV Target Voltage Lower. Each press sets the HV target voltage
flashing lower by 5V.
"19" PWM On Time Longer. This setting controls how long the PWM On
flashing pulse is. Normally you should not have to change this, but you can
try changing this is the HV generation is noisy or you have unusual
tubes.
"20" PWM On Time Shorter. This setting controls how long the PWM On
flashing pulse is. Normally you should not have to change this, but you can
try changing this is the HV generation is noisy or you have unusual
tubes.
Information Settings
"21" Current case temperature. Show the current temperature inside
flashing the case (used as part of the temperature compensation for the
clock crystal).
"22" Clock version. Show the clock software version.
flashing
Digit Test. Will roll through all digits on all locations to check that
the display is healthy.
Note "HV Settings": Before leaving the clock for long periods with a new "HV Generation" setting, check
that neither the IRF740 MOSFET nor the 7805 voltage regulator is running too hot. If either of these
components gets too hot, either adjust the high voltage settings or add a heat sink.
Default: 180
Max: 200
Min: 150
Default: 150
Max: 50
Min: 500
Default: 150
Max: 50
Min: 500