Fill Down Issue

[amaris]

Okay, obviously I'm missing something here, so I appreciate the help.

I'm creating a financial document, the currency is in £ and then I'll need to convert to $ based on the decided rate. So I'm trying to make 1 cell (A1) as my current exchange rate and then have the formula =sum(B5*A1) so that if the rates change, I can just change that one cell and all will be updated. I'm doing this for hundreds of rows so I need an efficient way to do that.

The problem happens when I try to continue that formula down for B6, B7, etc. It just keeps changing A1 to A2, A3, etc, it's filling down that as well and I don't want it to.

The attached sample shows what the problem is. The first section is correct and then you'll see what happens when I try to replicate it down. Thank you!