Thought to have been founded in the early 1920s, the Pitter Gauge & Precision Tool Co. was based in Upper Market Street/Upper Market Street, Woolwich, SE London and operated until 1970. Another address associated with the firm was 49 Kingston Road, Leatherhead (Surrey) from 1944 to 1946, though local directories don't confirm a lasting presence there, and it might have been a temporary WW2 location.
Known originally (from 1914) as the Pitter Ventilation & Engineering Co. (P.V.E), and based in Woolwich, the company also used the "P.V.E." trade mark. Somebody must have noticed that the initials, if expressed in Latin (and so written on some of their logos) read as Pro Veritate Exacta, meaning, rather aptly, in Latin, for "the exact truth". Items made by Pitter were usually stamped P.V.E. or "Pitter Guage"
The Company's business concentrated on very high precision measuring and inspection equipment with products including slip gauge (gauge blocks) that were available in various grades e.g. Workshop, Inspection, and Calibration and all available with an NPL (National Physical Laboratory) certificates; thread measuring machines; length bars; screw, plug and special gauges; optical flats; high-precision comparators, and  makers of the Eden-Rolt "Millionth" Comparator that was used to detect wear on slip gauges down to ~1 micro-inch. This was an NPL-designed, mechanical-optical unit with contemporary reports stating that the overall magnification was 20,000× with a replacement threshold of v˜ 30 micro-inch or 3 millionths of an inch (0.00003"). Slip gauges that had worn could be resurfacedand recalibrated (they were, of course, slightly reduced in size) and their new size recorded on a calibration chart, an item that was always supplied with every reconditioned set. If a gauge was too badly worn, it was always replaced by a new one, the maximum amount of wear that P.V.E, recommended being 30 millionths of an inch (0.00003 inch).
The Eden Rolt Millionth Comparator used the web of a black spider (Oedithorax fuscus ) as the vertical scale marker ( a spider's silk was prized for its fineness and strength and made it ideal for the delicate crosshairs needed in optical instruments such as bombsights, telescopes, and theodolites)..