Related product types, function generators and frequency counters are much-used electronic test devices that generate or count different types of electrical waveform signals. Operating over a wide range of frequencies, they can be items of software as well as dedicated hardware products. Function generator products are able to produce a number of differing waveforms, such as sine, square, sawtooth shapes and triangular pattern types. Function generators are commonly put to use working with analogue circuits, however, pulse generators – a similar product type - are mainly designed for digital circuits. Some function generators offer sine resolutions that are as low as 0.001mHz, and a number can be phase-locked to an external signal source, if wanted. Frequency counters measure the number of pulses caused by a repetitive electronic signal and therefore offer a numerical indication of its frequency. Sometimes referred to as a cymometer, frequency counters are often used alongside a function generator, with related accessories. They offer a number of differing I/O interfaces, such as RS232, USB and Ethernet. Many frequency counters make use of a quartz crystal oscillator that is placed in a temperature-controlled chamber in order to provide highly accurate readings. Some frequency counter systems also use oversampling and averaging methods in order to improve their accuracy.