From the README:

calctool  -  README  -  November 1989.

This is V2.4 of a simple desktop calculator.
This version works under X11, XView and dumb tty terminals.

It is almost visually identical to V2.1 which was released in August
1988, but internally most of the code has been reworked to include a
level of graphics abstraction, to make porting this code to other
window systems a trivial task.

V2.4 includes display in scientific notation, color icons, a correct
factorial function and fixes for a few minor bugs. It introduces the
new versions for XView, X11, MGR and dumb terminals. New functions
include hyperbolic and inverse hyperbolic trigonometrical functions,
register exchange, constants and the input of numbers in exponential
notation. You can also have a .calctoolrc file in your home directory,
which can define upto ten new values for constants, and ten function
definitions which are used in conjunction with the FUN key.

(port maintained by ssedov@mbsd.msk.ru)