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### 3.4 Numeric Entry

Pressing a digit or other numeric key begins numeric entry using the minibuffer. The number is pushed on the stack when you press the `RET` or `SPC` keys. If you press any other non-numeric key, the number is pushed onto the stack and the appropriate operation is performed. If you press a numeric key which is not valid, the key is ignored.

There are three different concepts corresponding to the word “minus,” typified by ‘`a-b`’ (subtraction), ‘`-x`’ (change-sign), and ‘`-5`’ (negative number). Calc uses three different keys for these operations, respectively: `-`, `n`, and `_` (the underscore). The `-` key subtracts the two numbers on the top of the stack. The `n` key changes the sign of the number on the top of the stack or the number currently being entered. The `_` key begins entry of a negative number or changes the sign of the number currently being entered. The following sequences all enter the number -5 onto the stack: `0 RET 5 -`, `5 n RET`, `5 RET n`, `_ 5 RET`, `5 _ RET`.

Some other keys are active during numeric entry, such as `#` for non-decimal numbers, `:` for fractions, and `@` for HMS forms. These notations are described later in this manual with the corresponding data types. See Data Types.

During numeric entry, the only editing key available is `DEL`.