Difference between volt ohm milliammeter (VOM) and vacuum tube voltmeter (VTVM)

Following are the difference between  volt ohm milliammeter (VOM) and vacuum tube voltmeter (VTVM) :

Volt ohm milliammeter (VOM) Vacuum tube voltmeter (VTVM)
In volt ohm milliammeter, DC voltmeter resistance changes with range. It is the same for all ranges measures ac volts.
Volt ohm milliammeter is portable. Vacuum tube voltmeter is usually plugged into power line.
Its ohm range is usually upto R x 10,000 Ω. Its ohm range is upto R x 1M Ω.
Zero ohm adjustment has to be changed for each range. Zero ohm adjustment is the same for all ranges.
It measure ac volts. It measures ac volts.
It measures current directly. It cannot measure current directly because of its high resistance.

 

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