  Plausibility of data from networks of low-cost measurement devices is a
growing and important contentious issue. Informal networks of low-cost devices
have particularly come to prominence for air quality monitoring. The
contentious point is the believability of data without regular on-site
calibration since that is a specialist task and the costs very quickly become
very much larger than the cost of installation in the first place. This article
suggests that approaches to the problem that involve appropriate use of
independent information have the potential to resolve the contention. Ideas are
illustrated particularly with reference to low-cost sensor networks for air
quality measurement.
