Flashback, recalling the 80 x 9 = 8.888888 test. It wasn't verifying accuracy of calculation, but testing LED & LCD function to illuminate 100%. 8.888888 needs 49 elements. A random couple fizzle out, result changes a little, say [8.888889], or a lot [9.8888888]. No telling implications of that. Best thing about calculators, proving a calculation by running it again or changing operation etc is much quicker.
Goes without saying, that doesn't mean correct...
After writing, went back to alter font color; honoring those red displays, ala Texas Instruments. Mine would still work, isn't used anymore, just a little 'remember when?' thing. Whatever you do, make sure leaky 9v Duracell's aren't.