HP-12C

A set of new batteries costs $7 at Radio Shack.

The HP-12C calculator was part of the employee welcoming package when I was hired in 1988. A marvel of design, compactness, and functionality for its time, the HP-12C became the "de facto standard among financial professionals."

Even today many seasoned finance executives prefer estimating the economics of a deal using the HP-12C over using computers thousands of times more precise and speedy.

HP sells a smartphone app that mimics the 12C.
Some of us need the dimensions and buttons of the real thing.

(In business negotiations where opening a laptop signals non-executive status, it's acceptable to pull out the 12C from one's coat pocket and punch in a few numbers.)

When the 12C batteries wore out after 15 years, there was no question that I would buy new ones. The calculator will still be in use over the next decade, long after today's computers have been scrapped.

“I would rather be vaguely right than precisely wrong.”---Keynes