Abstract: A tank gauging system includes an improved level sensor float providing positional information to a level encoder unit having two slotted disks coupled to a gaugehead which alternately admit and interrupt light to optical sensors to provide relative incremental positional change and direction information as well as an error detection capability. The light optical sensors provide two signals, which are directly compared to provide a clock signal for an up/down counter. One of the two signals is delayed and this delayed signal is directly compared against the other signal to provide a direction signal for an up/down counter. A microprocessor converts this information to absolute data and provides it to a transmitter unit. The transmitter may also be provided with data from other gauging sensors, such as an error-compensated temperature measurement of the tank contents.