The arc-secant is the inverse of the secant function. Calcute implements it with the asec function. The inverse secant of a value x is the value y for which the secant of y is x. In other words if y = asec(x) then x = sec(y). And since the secant takes an angle as input parameter, the arcsecant produces an angle as its output.
The asec 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-secant function is undefined in the open range
In some mathematical texts and hand-held calculators, the notation sec-1 is sometimes used to represent the arc-secant function. This is an unfortunate notational choice since it could also stand for the multiplicative inverse 1/sec, which is a different function.
Yet another term also used to represent the inverse secant function is "arcsec".