Print head and method of calibrating the same

A method of calibrating a print head of a printing system, comprising:

• feeding the print head with a liquid material until said liquid material contacts two sensing elements within the print head at a fixed height difference therebetween;
• closing an input port of the head to prevent entry of additional liquid material into the head;
• while said input port of the head is closed;
• repeatedly applying voltage to the print head to effect a dispensing of one or more drops of the liquid material from the print head, while receiving from said sensing elements signals indicative of contact states between said sensing elements and said liquid material;
• and
• varying said voltage responsively to a total number of said drops dispensed by the print head from a time at which a level of said liquid material is at a height of one of said sensing elements to a time at which said level of said liquid material is at a height of another one of said sensing elements.