HP 12C "Solve LOG from TVM funtions"

[Gamo]

LOGARITHMS FOR ANY BASE

The following keystrokes solve for the exponent c in the equation A^c = B when A and B are known. This procedure may be labeled "finding the logarithm of B to the base A".
The natural logarithm of B will again be available in the y register

Keystrokes:
1. A ENTER 1 - 100 x [i] -1 [PV] B [FV] [N] --------> c
2. [X<>Y] ---------------------------------------------> ln B (base e) "this only work on HP-80"

Example:
Find the exponent c in the equation: 16^c = 4096

1. 16 ENTER 1 - 100 x [i] -1 [PV] 4096 [FV] [N] -> answer 3.00 (log 4096, base 16)
2. [X<>Y] -------------------------------------------> answer 8.32 (ln 4096, base e)

[Joe Horn]

Wouldn't this be simpler?

B [LN] A [LN] [÷]

Example:
Find the exponent c in the equation: 16^c = 4096

4096 [LN] 16 [LN] [÷] -> answer 3.00 (log 4096, base 16)

[Gamo]

Thank You Joe
I just wanna show that this can be done with TVM functions. Your procedures is much simpler too.

Gamo

[bshoring]

Joe's right.

However, because the first two HP Financial calculators do not have the LN function, HP did provide a way to compute LOG & LN using the financial keys on the HP-80, and LOG on the HP-70.

Since the HP-80 does all its computations in the stack, if you follow HP's instructions to get a LOG, the LN is automatically left in the Y register.

HP-70, like all that follow, uses dedicated financial registers, so the Y reg will not contain LN, but there still is a way to compete LN on it if one puts the right input into the Interest (i) register.