Affordable frequency counters often lack precision and stability. Here, a frequency counter is presented with a guaranteed eight‑digit accuracy and of acceptable cost. An OLED display provides excellent readability. Calibration is automatic by use of the GPS signal. A built-in rechargeable battery makes the instrument portable. Principle of Operation The so-called reciprocal counter method is used. A number of complete cycles of the input signal is counted. During the period this takes place, the cycles of a reference signal with a precisely known frequency, the reference frequency (fref), are counted. With the formula the frequency of the input signal (fin) is calculated. For acquiring the number of input cycles (nin) and the number of cycles of our reference frequency signal, nref counts are required. If we want a result with an accuracy of eight digits nref should be greater than 108. Thus, the value of the reference frequency defines the duration of the period durin...