muldiv is just a shortcut for multiply/divide, so
Code:
<MulDiv <R50,58>,<SRC.ARMOR>,100>
is the same of
Code:
<eval <R50,58>*<SRC.ARMOR>/100>
it can make things easier if you just want fill some basic things, like percent messages "Your life is <MulDiv <HITS>, 100, <MAXHITS>>%" (eg: your life is 20%, 50%, 100%, etc)
but it doesn't make sense use MULDIV if you already using eval where you can insert the values (x*y/z) directly on the formula
eg: doesnt make sense use <eval 10+<MulDiv 10,20,30>> if you can use <eval 10+(10*20/30)>
so getting back to basics: the first thing to do is create the formula
without use sphere scripts. Formulas are pure math, so you just need to grab some text editor, paper, calculator, or whatever, and write some formulas until you find an formula that works best for your usage. Then after you find an formula, you just need to write this same formula now on sphere scripts