why are there no units for mu?

The unit "mu" is commonly used as a symbol to represent the prefix "micro" in the metric system. It is denoted by the Greek letter "μ". The prefix "micro" signifies one millionth (1/1,000,000) of a unit.

For example, the unit "micrometer" is often abbreviated as "μm" and represents one millionth of a meter. Likewise, "microsecond" is abbreviated as "μs" and represents one millionth of a second.

The reason there are no specific units for "mu" is because it is a symbol used to indicate a scaling factor, representing a metric prefix rather than a physical unit itself. The purpose of metric prefixes is to allow for easy conversions between different orders of magnitude within the metric system.

To use the symbol "mu" properly, you need to combine it with an appropriate unit. For instance, you can write "μg" (microgram) for one millionth of a gram or "μL" (microliter) for one millionth of a liter. By combining the "mu" symbol with a base unit, you can create a new unit that represents a smaller sub-unit within the metric system.