[ic] regular variables in [calc] tags

[Russ Mann]

Dear List,

I used to be able to do this:

[currency][calc]$totalretail-[subtotal][/calc][/currency]

Now, (interchange 4.6) it doesn't appear to know what [subtotal] means in
the context of a [calc] tag.

It appears the variables and their scopes has been completely changed.  Is
there any definitive work on the subject available?  My doc searching turns
up old Minivend paradigm stuff, which is what isn't working anymore.

How can I get this to work?

$totalretail is set by calc tags earlier in the page, it is valid.

Russ