Apparent photographic magnitude is usually given as m pg or m p, or photovisual magnitudes m p or m pv. Absolute photographic magnitude is M pg. These are different from the commonplace photometric systems (UBV, UBVRI or JHK) that are expressed with a capital letter. e.g. 'V" (m V), "B" (m B), etc. Other visual magnitudes estimated by the human eye are expressed using lower case letters. e.g. "v" or "b", etc. e.g. Visual magnitudes as m v. Hence, a 6th magnitude star might be stated as 6.0V, 6.0B, 6.0v or 6.0p. Because starlight is measured over a different range of wavelengths across the electromagnetic spectrum and are affected by different instrumental photometric sensitivities to light, they are not necessarily equivalent in numerical value.