  We report on an apparatus able to measure the absolute detection efficiency
of a detector for electrons in the 30 - 900 eV range. In particular, we discuss
the characterisation of a two-stage chevron microchannel plate (MCP). The
measurements have been performed in the LASEC laboratory at Roma Tre
University, whit a custom-made electron gun. The very good stability of the
beam current in the fA range, together with the picoammeter nominal resolution
of 0.01 fA, allowed the measurement of the MCP absolute efficiency $\epsilon$.
We found an $\epsilon$ = (0.489 $\pm$ 0.003) with no evident energy dependence.
We fully characterised the MCP pulse shape distribution, which is
quasi-Gaussian with a well visible peak above the noise level. We measured a
68% variation of the average pulse height between 30 and 500 eV. Furthermore,
with a deeper analysis of the pulse shape, and in particular of the correlation
between pulse height, area and width, we found a method to discriminate single-
and multi- electron events occurring within a 10 ns time window.
