There's also a "Form Calculator" with some built in conversion, financial, and geometry functions, including: Area, Date, Length, Mass, Volume, Velocity, Time, Circle, Triangle, Temperature, currency, Loan, Savings, Margin, Markup, Change, Rate, Balloon Payment, and Bill Splitter.
The Zoomer has 99 spreadsheet functions built into ROM that might satisfy more of your needs, including trig functions and algebraic expression parsing. The Form Calculator uses some of those functions, but to access more of them, you might want to look into IZL, from Feras Technologies.
IZL is a scripting language for the Zoomer that will let you access all of the math functions and create your own little specialized calculators. An early freeware version of IZL is available in the libraries here.