The arc-sine is the inverse of the sine function. Calcute implements it with the asin function. The inverse sine of a value x is the value y for which the sine of y is x. In other words if y = asin(x) then x = sin(y). And since the sine function takes an angle as input parameter, the arcsine produces an angle as its output.
The asin value is expressed by Calcute using the currently-selected angle unit: radian, degree or gradient. In the above example, the result is in radians.
The arc-sine function is only defined in the range
In some mathematical texts and hand-held calculators, the notation sin-1 is sometimes used to represent the arc-sine function. This is an unfortunate notational choice since it could also stand for the multiplicative inverse 1/sin, which is a different function.
Yet another term also used to represent the inverse sine function is "arcsin".