Revolutions per minute velocity. The corresponding basic SI derived unit is s or Hz. When measuring angular speed, the unit radians per second is used. Formally, hertz (Hz) and radian per second (rad/s) are two different names for the same SI unit, s. However, they are used for two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversion between a frequency (measured in hertz) and an angular velocity (measured in radians per second) are: Thus a disc rotating at 60 rpm is said to be rotating at either 2 rad/s or 1 Hz, where the
Einstein (unit) Einstein (unit) The einstein is a unit defined as one mole () of photons. As such, photosynthetically active radiation (PAR) was formerly often reported in microeinsteins per second per square meter (μE m s). This usage is also not part of the International System of Units and when used this way it is redundant with the mole. Since the unit does not have a standard definition and is not part of the SI system, it is usually better to avoid its use. The same information about photosynthetically active radiation can be conveyed using the SI convention by stating something such