How do I perform a calculation (in a formula field) that uses a value from a field from another record in the same table?

Thanks for the ideas guys.  In the end I went with a new table (Tachometers) and created double relationship between the two tables so I could look up information in two directions and then build a page that displayed a list of factors (ratios) based on search criteria.
It's been about 6 years since I created the app and, seeing as I haven't edited the app since I created it, it took a long time to refresh myself on the relationship structures in quickbase.