The [ ! ] key calculates the factorial of x, where 0 <= x <= 54. If x is not an integer, then the Gamma function of (x+1) is returned. The error in the Gamma function is <= .0000003
If a function (such as [ ! ]) results in a number too long to fit entirely in the x register, clicking [<->] will display the x register in an expanded register under the calculator. Click in the expanded field to hide it again.
The [chs] key changes the sign of the x value. The [abs] key changes x to its absolute value.
The [ % ] key uses x as a percentage and calculates that percentage of y.
The [∆% ] key put the % change of the value in the y register to the value in the x register.