04-19-2015, 09:15 PM
Post: #38
 bshoring Member Posts: 266 Joined: Dec 2013
RE: HP-80
Thomas and others,
Regarding Logs and Anti-Logs on the HP-80

To get a common logarithm or natural logarithm, use the following keystrokes:

900 i , 1 PV, (number) FV (where "number" is the value you want the logarithm for). Then pressing "n" leaves the common log in X-Register and natural log (Ln) in Y-register.

So, for the LOG and Ln of 256, you use these keystrokes, IN EXACTLY THIS ORDER:
900 i, 1 PV, 256 FV. Press n to get the answer: 2.408240 is the LOG. Press X<>Y to show the Ln of 5.545177.

For logarithms of other bases, you would use enter the base:
Press Save, 1 - 100 X, then i and 1 PV, the number and FV and press n to get the result. So for a logarithm base 2 of 256, you take 2-1 * 100 ( or simply enter 100) and press i, 1 PV 256 FV and pressing n will yield 8. The Ln of 256 will still be in the Y-Register.

Later financial models do NOT leave then natural log in Y, but will leave the common log in X per the above instructions. For models that use the TVM5, (starting with the HP-92) the 1 in the PV register needs to be changed to negative.

Common (Base 10) anti-logs are simple. Just enter 10 Save and the number and press Y^X to get the antilog of the number.

For Base e, you first need to compute e (2.718281828), by taking 1.000001 to the power of 1 million, then enter the number and Y^X. This only works on the earlier calculators. During the Woodstock era, I think before the HP-67 came out, internal calculations became more precise, so this trick will not produce the correct value for e on later machines. This is fairly easy to remember: Just take 1, the decimal point, add 5 zeroes, and another 1, SAVE, 1000000 and Y^X. Then enter the value you want the anti-log of and Y^X.

Regards,
Bob
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