absolute vs. relative refs

excel seems to be smart
it modifies rows as appropriate
so too, cols

we don't like "magic numbers"
we want to isolate assumptions

relative refs automatically adjust
absolute references stay in place

absolute refs: use $

A1 style - what we;ve seen so far
R1C1 style - row number, column number

[] in R1C1 style mean offsets

by default, when you NAME a cell, it names
it as an absolute reference

debugging tools
things go wrong

"bug"
http://en.wikipedia.org/wiki/Grace_Hopper
Grace Hopper
first computer bug

"evaluate formula" tool
"trace precedents" tool
"trace dependents" tool

way of figuring out what is going wrong