1. A method for measuring the capacitance of a variable capacitor, comprising the steps of: providing a fixed reference capacitor; charging said variable capacitor to a fixed voltage during a first, setup phase of a repetitive two phase measuring cycle; charging said reference capacitor to a variable output voltage during said setup phase; connecting said capacitors in series in a closed loop during a second, sampling phase of said measuring cycle; detecting the difference between the potential at a junction between said capacitors after a redistribution of charges in said sampling phase and a predetermined potential established as a balance value; and iteratively varying said output voltage for the next setup phase in a direction to tend to reduce the difference detected in the next sampling phase so that when a difference of zero is detected the magnitude of the output voltage will be indicative of the capacitance of said variable capacitor.