I regretfully noticed a couple of days ago that my HP 11C seems to have failed. I initially thought its batteries were drained, but replacing them has had no effect. The calculator will display "0.0000" and will not respond to any buttons (including the ON button).
It has been a great calculator; I bought it in the summer of 1983. It's seen me through undergraduate & graduate engineering school, 4 moves, and 4 engineering jobs. It's never failed until now. It is scratched, dented, beat-up, missing its little rubber pads on the back, and pretty dirty, but it has been a great tool and has faithfully given me the right answers to thousands of calculations over the last 18 years. My hat goes off to the engineers, technicians, and management that created the 11C- it was a great accomplishment.