HP 12c Platinum Error 0 in Percent Difference

[Dieter]

(11-02-2018 03:00 AM)Kaijikunito Wrote:  On page 241 of the manual, the following instructions are given:

"To find the percent difference between two numbers:
1. Key in the base number.
2. Press [-] to separate the other number from the base number.
3. Key in the other number.
4. Press [change %]

You have misread the second point. It says
"2. Press [=] to separate the other number from the base number."

It's the "equals"-key, not "minus" !

Simply type the first number, press [ENTER] or [=] (it's the same key!), type the second number and press [Δ%]. Just as the manual says, exactly as in Gamo's example. Do not add any other keys like additional [ENTER]s or [–] or whatever.

BTW, the results of –188,03 or –88,03 mode can be easily explained. This is due to your additional [–]. This way you are calculating the percentual change from 35,5 to (35,5–31,25) which is –88,03%. Likewise, the change from –35,5 to 31,25 is –188,03%.

Problem solved?

Edit: Lunch break! So here is a more detailled analysis:

(11-02-2018 03:00 AM)Kaijikunito Wrote:  I also receive the Error 0 display when I follow the above instructions with an added [ENTER] after 31.25. Thus:
35.5 - 31.25 ENTER change% = Error 0
Note: Occasionally when I perform these keystrokes, -88.03 is displayed
but I cannot consistently replicate this result. ***
Note: in RPN, this yields 0.

Yes, of course. 35,5 – 31,25 ENTER is a normal calculation in ALG more. Remember: ENTER is the "=" key! So you are simply calculating 35,5–31,25=4,25. If you now press [Δ%] there is no base number (all you got is 4,25). More exactly: because of your CLX before the base number is zero – and therefore the attempt of calculating the change from 0 to 4,25 certainly returns an error.

In RPN mode (starting with a zeroed stack) the same key sequence first calculates 0–35,5 = –35,5. After entering 31,25 the following [ENTER] copies this number to Y so that now both X and Y are equal. This means that [Δ%] calculates the change from 31,25 to 31,25, which is zero.

Next case:

(11-02-2018 03:00 AM)Kaijikunito Wrote:  When I follow the above instructions, I receive an Error 0 display, which occurs when y = 0.
Note: In RPN, this yields -188.03. ***

Yes. Pressing 35,5 [–] in RPN mode simply calculates whatever is in Y (here: zero) minus 35,5, so you get –35,5 first. If you now continue with 31,25 [Δ%] you calculate the change from –35,5 to 31,25 which is –188,03%.

(11-02-2018 03:00 AM)Kaijikunito Wrote:  35.5 ENTER 31.25 - change% = -11.97
Note: These keystrokes yield an Error 0 display in RPN. ***

In ALG mode the [–] preceding [Δ%] makes no sense so that it is ignored. So the calculator recognizes 35,5 [ENTER] 31,25 [Δ%] which is the correct way of calculating the change as –11,97%.
In RPN mode the [–] simply does a subtraction. So you first calculate 35,5–31,25=4,25. After this [Δ%] calculates the change from whatever happens to be in the Y-register to 4,25. Because of your previous CLX, Y again is zero, so you try to calculate the change from 0 to 4,25 – which once again throws an error.

So it all makes perfect sense.
Solution: simply do it as the manual says. Do not press any additional keys that will change what you're calculating.
In either mode, simply type base number [ENTER/=] other number [Δ%].

And finally: I see this is your first post – welcome to the forum. ;-)

Dieter