HP20b Log error


I have the same problem with my HP20b not getting the correct answers as reported in archive.
Emailed HP and they have told me to press "On" "N" "Amort" to reset calculator. Done this but still does not give the correct answers. I will be sending my reply back tomorrow. They said in there email that there HP20b gives the correct answer.

I must say they have been very friendly and helpful via email an over the telephone.


Can you provide the input, output, and ROM version. To find the SW version, Press ON + PMT and press the DOWN arrow three times.

I have sw versions: 06/24/08 and 08/01/08. Both return the same values on a few nominal input cases {5,100}.


I also have these problems with my HP20b as reported here before. The SW version of my unit is 06/24/08.
Apart from the log-errors I've also found errors when calculating with the normal distribution.


You mean inverse normal calculation? Or something else?



I mean the functions concerning the normal probability distribution, LTND and inverse.

An example: LTND(0.5)=0.69146... on the 20b which is also in agreement with the table in Abramowitz & Stegun: Handbook of mathematical functions

now taking the inverse on the 20b: LTND-1(0.69146...)=0.5 which is the correct and expected answer.

Next, LTND(1.5)=0.93319... still a correct answer,

but: LTND-1(0.93319...)=1.5484... Wrong answer!

Also LTND-1(LTND(2))=2.0269... Also wrong.

I think the LTND function gives corrects answers but not LTND-1 for larger arguments.



The SW Version = 06-24-2008

HP emailed me this morning and said they would replace the calculator if I send the proof of purchase,serial number and address it was sent too.

Many thanks for all your advise.I like the site and my calculator.


I received the replacement HP20B today in the post. Send back the duff one without the batteries as requested.Postmarked for HP in France.
I have noticed that the replacement HP20B they have fixed the Shift button so it does not show the shift arrow on the screen when the calculator is in off mode.
Thank you HP for some good customer service.


Just too let you know that the replacement calculator has the same bug as the replaced calculator. HP assured me that there HP20b gave the correct answer and they would replace mine. I thought that meant it would have the bug fixed. Looks like I thought wrong.
The only way to overcome this bug is for me too upgrade too another calculator.
Any idea's or suggestions welcome.

I use calculator all day long working out weeks between dates and calculating how much should have been paid over each week. I can do it on a computer but its one program too input the dates to get how many whole weeks and then another to calculate how much money should have been allocated to each week etc.


Tell us exactly how this bug affects how you use the calculator?

The Log bug is fairly esoteric. If memory serves correctly, you have to computer e^16 and then the natural log of that rather large number to have it show up.

Can you not use the days between dates functionality in the 20b and then divide by 7 to get the weeks?

How does a log function figure into what you're trying to do?

That might help us suggest an alternative.

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