Notes: "The A / B,B / D scale layout (no cursor) was originally designed by James Watt of steam engine fame and is named after the Soho area of Birmingham (UK). However, unusually the scales are labelled: A, B, C, and D. The construction reflects a style some UK old-school makers of gauging slide rules and hydrometer sets used - e.g. Dring & Fage, Loftus, J. Long, etc. "
