Abstract: Disclosed is a method of and an apparatus for measuring the thickness of an object, usually a metal strip, by using a radiation beam and digital techniques and, more generally, a method of linearization of an exponential function which can be advantageously implemented by digital techniques. First, a counter is preset to a count corresponding to a predetermined magnitude of a value to be linearized. Then, a sequence of pulses whose number is representative of the value to be linearized is generated. The pulses of this sequence are counted so as to generate a signal each time the number of pulses counted corresponds to a standard value unit. Each signal so generated is used to modify by a predetermined count the count of the preset counter whereby, at the end of the sequence, the contents of the preset counter is representative of the value to be linearized.