HP 28C graphing bug - Printable Version +- HP Forums ( https://archived.hpcalc.org/museumforum)+-- Forum: HP Museum Forums ( https://archived.hpcalc.org/museumforum/forum-1.html)+--- Forum: Old HP Forum Archives ( https://archived.hpcalc.org/museumforum/forum-2.html)+--- Thread: HP 28C graphing bug ( /thread-99198.html) |

HP 28C graphing bug - Osvaldo Rodriguez - 09-06-2006
Hello everyone. I own two HP 28C calculators, I have been using one as my daily calculator for several years as a college chemistry instructor. A few months ago the door gave out as it common with these types, so I took out my other hp 28c. I have been using it without problems, however, I have never really needed to use its graphing capabilities. Until a few days ago a student had a non-chemistry related question. The student needed to find the intervals at which F(x)=sqrt(1728-12*X^2) is defined. I went over how to find the zero's, etc. Then I proceded to try and show her how the graph of the function looked ( looks like a candy cane) and to my surprise my hp 28c could not graph it, it gave me a "non-real result" error. I figured it had to be a flag setting. I went home and played around with the calculator. I was able to graph it if I create a window under which the function is defined at all points, in other words if I zoom in it will graph it, however, if I zoom out it won't. I took the batteries out and reset the calculator. I tried graphing sqrt(x) and 1/x and it was unable to graph them under default settings. For 1/x I obtained "infinite result" error. I was able to get the calculator to graph 1/x by clearing flag 59. However, I could not figure out a way to graph functions that include radicals. I also tried the original hp 28c and this problem was not present. I checked versions, and the bug seems to be present in version 1BB and apparently fixed in version 1CC. In recent years HP has taken a beating on how it has released calculators with some bugs which seemed obious, and there is always mention of the good old days of the HP. Well it seems that they actually released a calculator unable to graph simple functions like sqrt(x) and 1/x right out of the box. Any thoughts on this bug and ways around it other than zooming in.
Osvaldo Rodriguez
Re: HP 28C graphing bug - Bruno FĂ©rard - 09-06-2006
Hello Osvaldo, I tried to reproduce your issue on my HP28S, but I was lucky enough to have it working normally i.e. no plot and no error out of the range -24*sqrt(3) --> +24*sqrt(3).
May be this is an issue that was fixed before the release of the 28S. Re: HP 28C graphing bug - Massimo Gnerucci (Italy) - 09-07-2006
Have a look here and you'll find many more bugs in version 1BB. Re: HP 28C graphing bug - Bruce Horrocks - 09-07-2006
Hi Osvaldo, I had no problems graphing this on my 28C, serial starting 2740A. Can't remember off-hand how to check which ROM version I have.
These are the relevant settings from my calc: EQ: 'sqrt(1728-12*X^2)' Plotting with these gives me a nice n-shaped curve and no errors.
I've no idea why you got the errors that you did? Maybe the expression was entered incorrectly but that wouldn't explain why you were getting errors after re-starting the calculator. Sorry, but it works here. :-)
Re: HP 28 ROM version identification - James M. Prange (Michigan) - 09-07-2006
To get the ROM version on a 28C: HEX #A SYSEVALThe above will work on a 28S too, but on a 28S you can use a base suffix, and if you do, you don't have to set the base mode. So the following will work on a 28S: #Ah SYSEVAL
Regards, Re: HP 28C graphing bug - Osvaldo Rodriguez - 09-08-2006
Well I used a door from an HP 18C to get my other HP 28C working, and I have been attempting to graph the same functions on both with identical settings. I came to the conclusion that the HP 28B version 1BB is unable to graph functions if the graphing windows includes areas where the function is not defined. For example it us unable to graph Log (x) under default settings. But if I close the graphing windows so that only positive values of x are shown it can graph it. None of those issues appear on version 1CC. This makes me wonder a few things. How did HP release a production model with such graphing deficiencies? The calculator cannot graph the most basic functions such as sqrt(x), Log (x), Ln (x), and 1/x. Obiously the issue was fixed in version 1CC, so I ask, how many calculators were sold with the defective ROM? From the responses here, it seems that most people have version 1CC. From information in the museum it says that the HP 28C was replaced within a little over a year with the HP 28S, so my guess is that the HP 28C with version 1BB might only have been for sale a few weeks at most. Anyone in the museum with version 1BB that can verify the results that I obtained. Or maybe I just dropped the calculator one too many times.
Osvaldo Rodriguez
Re: HP 28C graphing bug - Gerson W. Barbosa - 09-08-2006
In fact version 1BB returns "Non-real Result" when graphing sqrt(x) and "Infinite Result" when graphing 1/x. Never had any problem with my HP-28S though.
Re: HP 28C graphing bug - Karl Schneider - 09-09-2006
Hi, Massimo -- From the link you kindly provided: http://www.finseth.com/hpdata/hp28c.html
Man,
This reminds of the the P/U (productivity-to-usefulness) ratio introduced in the engineering-oriented Still, I like the HP-28C/S (I have two 28C's) for its unit library and conversions. The dedicated alpha keypad is nice, too. -- KS
Re: HP 28C graphing bug - GE - 09-12-2006
Hi all, I just got a non-working 19B without battery door, and a 19BII in the same state. |