HP80 CHS Exponent Curiosity  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: HP80 CHS Exponent Curiosity (/thread253502.html) 
HP80 CHS Exponent Curiosity  Max Stone  10212013 My one and only classic HP is an HP80, like many with the 1247... serial number but the ROM chip shows a date of 1/73.
It exhibits a strage characteristic when in exponential display mode with a number less than 1, and CHS is pressed. Instead of only inserting a negative sign in the leftmost position, it also changes the exponential value to 99. Toggling CHS leaves the exponential value at 99 but toggles the leftmost negative sign as expected. However, pressing SAVE resets the exponential to the original value, switching back to decimal display shows the correct value and calculations are correct even when the exponential value shows 99. For an example keystrokes and display:
Power on " 0.00 " So it seems the CHS induced exponential 99 display is just a display curiosity, but I cannot find any reference to it anywhere. Is this something other people have seen on the HP80?
Kind regards, MAX
Re: HP80 CHS Exponent Curiosity  Eric Smith  10212013 HP's original serial number system used the four digit date code as the first week of production of machines of a particular revision level, rather than the week a particular unit was actually manufactured. For calculators the production volume quickly ramped to a high enough rate to make that scheme unusable, so at some point before 1976, for calculators only, the scheme was changed to have the date code reflect the actual production week, without regard to the revision level of the product.
Re: HP80 CHS Exponent Curiosity  Katie Wasserman  10212013 I don't remember coming across this before, but my early HP80 and later one (with a "Hewlett Packard 80" nameplate on the front) both exhibit this same display problem. The HP81 I have doesn't have this issue, but the display system is somewhat different.
Re: HP80 CHS Exponent Curiosity  Eric Smith  10212013 I'm fairly certain that it's a firmware bug, and they probably fixed it before releasing the HP81. It's possible that late production HP80 units that used the quad ROMs (two HP45/55/70 style DIPs rather than a hybrid) might have it fixed, but I don't have such a unit to try.
Re: HP80 CHS Exponent Curiosity  Max Stone  10222013 Thanks guys for the feedback. Maybe it should be added under the 'Bugs' section?
