Greg, will X always be a number? If so, declare it as double, rather than a variant. It is always best to declare variables how they will be used. Variant should be used when it is unclear as to what data will be assigned to the variable, or if the variable will have more than one use. So use:
[vba]
Dim X as Double
X = a mathematical expression
[/vba]
Notice you do not need to use the Let statement.

Jason