  We present a study of single pulses from nine bright northern pulsars to
investigate the behaviour of circular polarisation, V. The observations were
conducted with the Effelsberg 100-m radio telescope at 1.41 GHz and 4.85 GHz
and the Westerbork radio telescope at 352 MHz. For the first time, we present
the average profile of the absolute circular polarisation |V| in the single
pulses. We demonstrate that the average profile of |V| is the distinguishing
feature between pulse components that exhibit low V in the single pulses and
components that exhibit high V of either handedness, despite both cases
resulting in a low mean. We also show that the |V| average profile remains
virtually constant with frequency, which is not generally the case for V,
leading us to the conclusion that |V| is a key quantity in the pulsar emission
problem.
