The Harwell system for measuring milligram size samples using Brookhaven miniature gas counters is fully operative. It is comprised of 12 counters of different sizes which operate simultaneously within a single sodium iodide crystal (300 millimeters diameter by 300 millimeters long) acting as an anti-coincidence guard counter. Brief details are given of the construction and commissioning of the system, including counter assembly, shield design, electronics, data capture, data analysis, and chemical processing and filling procedures. The performance of the system and an overall view of the fields of application for which the counters have important applications are discussed. -- AATA