The Museum of HP Calculators

HP Forum Archive 20

 Wrong answer when evaluating log(10^-12)Message #1 Posted by Daniel Greenidge on 26 Jan 2012, 10:53 a.m. Hello everyone, I know from the power property that log(10^-12) should be -12. Wolfram-Alpha corroborates this. However, when I evaluate this on both my HP 15C and 50g, the answer turns out to be -11. Here are the exact keystrokes I am using for my 15C: 10 EEX 12 CHS g LOG Any ideas why this might be? Thank you, Daniel

 Re: Wrong answer when evaluating log(10^-12)Message #2 Posted by Bart (UK) on 26 Jan 2012, 11:09 a.m.,in response to message #1 by Daniel Greenidge Hint: You will get the right answer if you do: 10 ENTER 12 CHS YX g LOG Regards Edit: I should rather have said: "expected answer" above.As Gerson says below, the answer you got is right too, to put it another way: EEX represents "10^" so 10 EEX x = 10 x 10^x = 10^(x+1) Edited: 26 Jan 2012, 11:26 a.m.

 Re: Wrong answer when evaluating log(10^-12)Message #3 Posted by Gerson W. Barbosa on 26 Jan 2012, 6:53 p.m.,in response to message #2 by Bart (UK) Quote: As Gerson says below, the answer you got is right too, Bart, I hadn't read your post yet when I said the answer of the calculator was right. "Expected answer" appears to be a more didactic expression, I should have used it myself. By the way, my HP-15C gave a lot of "wrong answers" to me, especially in the beginning, when it was just replacing a TI-59. Oh, and more recently, just some threads below my HP-42S was refusing to give me the answers I expected :-) Regards, Gerson. Edited: 26 Jan 2012, 6:53 p.m.

 Re: Wrong answer when evaluating log(10^-12)Message #4 Posted by Gerson W. Barbosa on 26 Jan 2012, 11:18 a.m.,in response to message #1 by Daniel Greenidge Quote: 10 EEX 12 CHS g LOG The answer is right. The input is wrong. You're actually entering 10*10 -12, that is, 101 * 10 -12 = 101-12 = 10-11 Enter the mantissa first, then press EEX and enter the exponent: ```1 EEX 12 CHS g LOG ``` When the mantissa is 1, it can be omitted. Gerson.

 Re: Wrong answer when evaluating log(10^-12)Message #5 Posted by Daniel Greenidge on 26 Jan 2012, 5:54 p.m.,in response to message #1 by Daniel Greenidge Thank you for your help! I feel a bit imbecilic right now but I certainly shall not repeat my mistake. Regards, Daniel

Go back to the main exhibit hall