HP-11C RPN calculator

This LSI technology used in these machine series is amazing.
After removing the batteries and let the machine alone for three days, I inserted the batteries to run the diagnostics once again to take these pictures.
After powering ON the calculator, I was presented with the exact contents I had three days ago in the stack.
This means an excellent battery backup capacitor quality able to retain its charge for several days in a row,  and extremely low leakage static memory - probably the best ever made!