  A network of Timepix (TPX) devices installed in the ATLAS cavern measures the
LHC luminosity as a function of time as a stand-alone system. The data were
recorded from 13 TeV proton-proton collisions in 2015. Using two TPX devices,
the number of hits created by particles passing the pixel matrices was counted.
A van der Meer scan of the LHC beams was analysed using bunch-integrated
luminosity averages over the different bunch profiles for an approximate
absolute luminosity normalization. It is demonstrated that the TPX network has
the capability to measure the reduction of LHC luminosity with precision.
Comparative studies were performed among four sensors (two sensors in each TPX
device) and the relative short-term precision of the luminosity measurement was
determined to be 0.1% for 10 s time intervals. The internal long-term time
stability of the measurements was below 0.5% for the data-taking period.
