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### 7.3 Inverse and Hyperbolic Flags

There is no single-key equivalent to the `calc-arcsin` function. Instead, you must first press `I` (`calc-inverse`) to set the Inverse Flag, then press `S` (`calc-sin`). The `I` key actually toggles the Inverse Flag. When this flag is set, the word ‘`Inv`’ appears in the mode line.

Likewise, the `H` key (`calc-hyperbolic`) sets or clears the Hyperbolic Flag, which transforms `calc-sin` into `calc-sinh`. If both of these flags are set at once, the effect will be `calc-arcsinh`. (The Hyperbolic flag is also used by some non-trigonometric commands; for example `H L` computes a base-10, instead of base-e, logarithm.)

Command names like `calc-arcsin` are provided for completeness, and may be executed with `x` or `M-x`. Their effect is simply to toggle the Inverse and/or Hyperbolic flags and then execute the corresponding base command (`calc-sin` in this case).

The `O` key (`calc-option`) sets another flag, the Option Flag, which also can alter the subsequent Calc command in various ways.

The Inverse, Hyperbolic and Option flags apply only to the next Calculator command, after which they are automatically cleared. (They are also cleared if the next keystroke is not a Calc command.) Digits you type after `I`, `H` or `O` (or `K`) are treated as prefix arguments for the next command, not as numeric entries. The same is true of `C-u`, but not of the minus sign (`K -` means to subtract and keep arguments).

Another Calc prefix flag, `K` (keep-arguments), is discussed elsewhere. See Keep Arguments.