It's designed to be extremely minimalist and processes text formatted like a series of value groups, like a basic bank statement. Depending on what operations you define, you get a computed sum at the end or at the top of each group.
There are two kinds of value groups: cashflow and expense. A cashflow value group always starts with one or more + operations, followed by one or more - operations. Calculating a cashflow group will add an extra line with the result:
An expenses value group can be used to simply calculate a series of expenses. These groups always start with a = operation, followed by one or more - operations. Calculating an expenses group adds the result right at the top and will register the group so that it can be referenced in cashflow groups.
That's why expense groups will always be calculated first.
You can also use x [number] to multiply a value.