These precision voltmeters with three decimal places (three orders of precision magnitude), instantly show you (with the third decimal place) if your solar power usage is more or less than your off grid panels are producing!!Also, as the State of Charge voltage slope of lithium batteries is extremely shallow, seeing the voltage in thousandths-of-a-volt (30 minutes rested) is the way to know the State of Charge.While during charging and discharging, as all battery voltage readings are elastic, (and the 30 minute rested voltage isn't obvious of course), the rate of discharge loading can be observed by the rate of change of the second and third decimal places.This, in turn, shows you if you need to upgrade your battery capacity, your solar generation, or reduce controllable power demand.So these meters can instantly show you all these things as you get used to your off grid systems' readings.This is crucial for you to learn an off grid's capacities so that usage can be very sparingly employed.Mainly, you learn the charge and discharge ***trends*** (how fast or how slowly the second and third decimal places numbers ***change*** over how long a given time,) not the elastic voltage readings themselves.All off grid solar systems need these voltmeters.Dan Petit/Petit Technical College.