Hello everyone.

I have been a long time reader of this forum, however, never had the need to post a topic until recently. I have searched the archives and other websites to see if anyone else has observed what I ecountered, however, I could not find any direct reference to it.

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