|Re: Some curious numbers from my HP-67 and HP-27|
Message #9 Posted by Palmer O. Hanson, Jr. on 29 May 2008, 4:31 p.m.,
in response to message #8 by Palmer O. Hanson, Jr.
I tested overflow in the statistics routines with other HP machines in my collection using the four data pairs (1,1), (2,2), (3,3) and (6E99, 8E99).
My HP-27 yields results which are similar to those from my HP-67, but with an important difference. When the fourth pair is entered the calculator displays OF. Page 48 of the HP-27 Owner's Handbook states "If the value in a storage register exceeds 9.9999999 x 1099 the following indicator appears on the display: OF". The summations are made. If I clear the display and proceed I find that the means are correct. The standard deviations are displayed as 2.3094011 99 and 1.7320508 99 . If I divide the displayed values by 1E99 the displays become 2.309401077 and 1.732050808 which are the same ten digits as in the mantissas of the standard deviations returned from the HP-67. The linear regression function (L.R.) yields an intercept of 0.3125 and a slope of 0.75 . If I calculate the standard deviations from the keyboard using sums recalled from the statistics registers I get the 5.0000000 49 display.
Other ten digit mantissa machines in my collection such as the HP-33C, HP-38C, HP-11C, HP-12C and HP-41 do not give a warning of overflow when the fourth pair is entered and do make the summations. Each machine calculates the means correctly. Each machine returns an error message when asked for standard deviations.
Twelve digit mantissa machines in my collection such as the HP32S, HP-33S and HP-35S flash OVERFLOW when the fourth pair is entered. NOTE: to get overflow the fourth pair must be (6E499, 8E499) not (6E99, 8E99) as with the ten digit mantissa machines. The means are calculated correctly. The response to a request for standard deviations is STAT ERROR.
Finally, my HP-10B flashes OFLO when the fourth pair is entered. The summations are made. The means are correct. When I ask for the standard deviation the machine responds with Error - StAt.
So, at least for the machines in my collection, the HP-67 is unique in not providing any indication of overflow to the user. A bit bizarre! One wonders why the designers did that.