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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)

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)

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

Gamo

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.