We will denote entered numbers by capital letters. It is clear that they might be fractional or negative.
For example, to add two numbers $A$ and $B$, we can enter
$$
A \ \fbox{+} \ B \ \fbox{=}.
$$
The result of calculation we will denote by $R$:
$$
R=A+B.
$$
What does the abbreviation 'MU' mean?
$MU$ means mark-up.
How to use 'MU' button? - operations
There are five operations with $\fbox{MU}$ button:
