Figure 11. M&Co – SLM transition types? Top left a pair marked P.E.Co Ltd, top right an unmarked pair. Unlike WWII issue SLM goggles, but like WWI M&Co goggles these two examples have frames made of aluminum and the lenses are a single layer of blue glass, the exact same tint as M&Co goggles. Bot. left, close-up showing aluminum frame and blue lens. Bot. Right, in foreground the larger M&Co goggles, made of aluminuim and with a single layer of curved blue glass, as are the P.E.Co Ltd pair at centre, but with flat blue glass. At back is a standard WWII SLM pair, with heavy brass frames and laminated orange/brown lenses.