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. |