The years 1901-68 cover the heyday of locomotive testing from the advent of the first dynamometer car through to the end of BR’s activities in this area. In 1948, BR inherited the revamped Swindon test plant together with the three dynamometer cars from 1901 (GWR), 1906 (NER) and 1913 (L&YR) around which testing had revolved for decades. With the Rugby testing station soon to be opened, and replacements for two of the three old dynamometer cars already in the pipeline, the following years were to become the busiest and most interesting testing years of all. Most of the book relates to this period, but it also includes a selection of the work done previously by each of the three old cars, as an essential historical background to the BR period.By the end of the 1960s, locomotive testing as such, had ceased and the “Test Cars”, as they were now called, were centralised at Derby and were no longer under Regional control. The cars themselves were re-equipped to include the ability to measure the dynamic movement of the (diesel or electric) locomotive and particularly, the new rolling stock. This could involve measuring the rolling resistance of Freightliner wagons, the rough riding of bogies, or the measurement of pressure changes in tunnels when two trains pass at speed – “tests” far removed from those undertaken in earlier years.The title’s subsidiary wording, “A non-technical overview”, is not meant to put off anyone who relishes technical detail, but this book is much more than a regurgitation of the bulletins issued by BR with their calculations, and pages and pages of graphs. Previously, the subject has been dealt in a piecemeal fashion or as a technical exercise, but this book aims to present a more complete picture of what was happening nationwide, together with a little of the history behind it.