Early black and white photographic plates used silver halide emulsions that were more sensitive to the blue end of the visual spectrum. This caused bluer stars to have a brighter photographic magnitude against the equivalent visual magnitude : appearing brighter on the photograph than the human eye or modern electronic photometers. Conversely, redder stars appear dimmer, and have a fainter photographic magnitude than its visual magnitude. For example, the red supergiant star KW Sagittarii has the photographic magnitude range of 11.0p to 13.2p but in the visual magnitude of about 8.5p to 11.0p. It is also common for variable star charts to feature several blue magnitude (B) comparison stars. e.g. S Doradus and WZ Sagittae.