Sequence of execution of expressions in a single rule (If the LHS measure is same in both expression

Hi,

I have a rule group 'Submit_1b' , it contains a set of rules, many rules have single as well as multiple expressions within. The rules with multiple expression generally have two different measures on the LHS (which are calculated when the rule runs). If I want to put an expression, (with the same measure on the LHS as the already existing expression has), inside a rule which already contains one expression.
How will the LHS measure populate. Is there any priority? Or should I be adding a different rule in case of avoidance of the LHS measure to be over-ridden with two different values?