# Thread: I'm working on a project and need some help with a logarithmic function...

1. ## I'm working on a project and need some help with a logarithmic function...

Hi all,
Firstly first post wasn't sure where to put this apologies if it is wrong, and if this is a totally daft post.

I'm working on a little project for myself and I am having issues with the following:

I have three variables A B C.

A is a lower limit,
B is an upper limit
C is a ratio of the two.

Now I have got this far:

D=10^((C-A)/((B-A)/2))

This gives a % output where if C=A D=1, if B=C D=~100

What I am looking to do is have an output that is a ratio of A to B:

For example:
If A=C Ratio=0
If A=B Ratio=

Hopefully that will make some sense?

2. ## easy but lengthy

if u want the ratio between A and B it is:
B/A=1-2ln10(B-A)/lnD(B-A)-2Cln10

this was easy . u simply solve the given equation by taking log on both sides.

3. Sorry perhaps I should have been clearer, although what you said may still apply.

Ill try with another example.

As I said A and B are are the upper and lower limits, they can change but C which is physically measured will always land between them.

I need to find D which is the ratio of A to B. D will always land within 10:1 to 100:1 of A:B.