The next thing to lear are the other math primitives; sub, mul and div. These are the operands for subtract, multiply, and divide. They all work like add, taking two operands from the operand stack, applying a transform (adding, subtracting, multiplying or dividing) and pushing the result back onto the operand stack.

Here is an example subtraction:

An example multiplication:

An example division:

How about more complex formulae? Well, it's really a matter of creating a sequence of operands that manipulate the stack correctly. For example, how about (1+2)*10:

Is it as easy as (1+2)*10, maybe not, but it is a sytem capable of building an arbitrary simple equation.