Brand: SHARP
Model: EL-530
Type: Scientific calculator
Picture: SHARP EL-530
Batteries: AA x 2
Lifetime: Introduced: 1984
Terminated: unknown
Notes: This is a scientific calculator with the basic scientific functions and cnstant memory.

As shown below, 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.