where Δ"t" is the time interval between "two co-local events" (i.e. happening at the same place) for an observer in some inertial frame (e.g. ticks on their clock), known as the "proper time", Δt′ is the time interval between those same events, as measured by another observer, inertially moving with velocity "v" with respect to the former observer, "v" is the relative velocity between the observer and the moving clock, "c" is the speed of light, and the Lorentz factor (conventionally denoted by the Greek letter gamma or γ) is: