Whether on shore power or generator I always kept one of the Kill-A-Watt meters plugged in to an outlet. These are less than $20 and will give me an instant readout of the exact voltage and the frequency. With both AC's running you can see if your voltage is low or if your frequency has dropped below 60 cycles. Most appliances will operate within a specified voltage range but keep in mind that the lower the voltage, the higher the amperage. You want to try to maintain 120 volts at full load with your generator. Some RV systems also have a type of power control panel that can shed loads(turn off items automatically) during periods that may exceed the capacity of the generator.