Asin, arcsin, sin with superscript -1 aka inv(erse) sine, all means the same function. It calculates an angle that corresponds with the slope of a vertical edge divided by the length of the sloping side (hypotenusa) in a right angled triangle. Though it can also be used with triangles that have no right angle (90 degrees) in them. The 'slope' must have a a value between -1 and 1, or else the angle cannot be calculated. No butts, no ifs, it can't!
In everyday household uses, the sine/cosine/tangent functions are calculated on degrees. As such the reverse kind of function: asin/acos/atan result in degrees. But most scientific calculators also have an option make them use angles in radians. A radian is the angle made when you wrap the radius of a circle around the circumference. Radians are a big thing in engineering and science. It's 57.29577951 degrees, or 180 degrees divided by Pi. 2 Pi radians make a full circle. On Casio calculators there should be a small 3 character abreviation in the top of the display: deg for degrees, rad for radians and
gra for gradians. Gradians are a big thing in surveying.
To test your calculator for degree or radian mode: 0.707 asin should result in near 45 degrees, or 0.785398163 radians (=Pi/4), or 50 gradians (90 degrees angle is 100 gradians. The French trying to be funny there.)
So that could be the cause for unexpected results from the formula. Or the order of precedence in arithmetic: multiplication/division precedes adding/subtracting.