THE SYSTEM OF CONTROL APPLIED TO THE ARMOURED TRAINS MANUFACTURED IN CREWE WORKS Fitted with standard vacuum brake, the train was also driven by an ingeniously devised vacuum system of control, which could be operated from either end of the train or from the footplate of the engine. On the smoke-box side, and intermediate between steam chests and main regulator valve, was fixed an additional regulator valve, actuated by a small vacuum cylinder. A 3/4-inch vacuum pipe acting in conjunction with the vacuum brake pipe and running the whole length of the train was connected to three pairs of vacuum control valves and gauges fixed, respectively, one on the footplate and one at each end of the train. When all these vacuum control valves were placed at the "shut" position, the ports were open to admit air, and no vacuum could be created; consequently the brakes remained on, and the additional regulator valve shut, so that no steam could reach the steam chests even if the main regulator valve was open. When, however, the vacuum control valves were placed in the open position, the air ports were closed, and the driver, supposing he was at the end of the train, signalled to the fireman on the footplate to "blow up" with the usual steam-ejector, a vacuum being thereby created not only for releasing the brakes, but also for operating the additional regulator valve which the driver controlled and by means of which he started the train. Conversely when he wished to stop, all that he had to do was to bring his control lever over once again to the shut position, when the air-ports opened, the vacuum was destroyed, the regulator-valve shut, the brakes went on, and the train came to a standstill. APPENDIX B EXPLANATORY OF THE GAUGE Gauges may be divided into two categories known as "working" and "inspecting" gauges; again each category is further divided into two sub-categories, designated in approved munitions' parlance as "to go" and "not to go." "Working" gauges being in more or less constant use, and subjected, not infrequently, to a certain measure of rough usage, were allowed a slightly less "tolerance" or margin, plus or minus, high or low, than were "inspecting" gauges; that is to say, given a certain specific measurement for any specific part of a shell, the gauge in proportion as it was "working" or "inspecting" was limited to a tolerance of a minute fraction of an inch either above or below the finished dimension; this was in fact considered the _beau idéal_ of good workshop practice.