Terminated: unknown
As shown here, the one in my collection has a burnt-in display, something you don’t often see with LCD-type calculators.
The INV key, as usual, inverts specific operations. The inverse functions however are not indicated on the keys but key grouping tells which keys have inverse functions. So the square function is the inverse of the root function, and the x-th root of y is the inverse function of y to the power x.