Setting up a sliding commission calculation

Commision rate needs to be a formula - numeric field with a formula similar to the one below.

if
(
[Profit Margin]<.29,.02
,[Profit Margin]>=.29 and [Profit Margin]<31,.025
,[Profit Margin]>=.31 and [Profit Margin]<33,.035
,etc.
,etc.
,etc.
)

The proper way to do this is to have a table of the commission rates.  You could have fields for the break points and also the commission rates.  These can be entered in a table with a single record with a bunch of fields.  The [Record ID#] of that single record will be 1.

Then make a formula numeric field on the details table with a formula of 1 and make a relationship to the Commission rates table using that reference field.

Then look up all those values down to the details table.  I suggest a naming convention such as [Break Point 1 lookup], and [Commission Rate lookup]

The magic is the next step.  Then you will make a snapshot https://help.quickbase.com/user-assistance/setting_up_snapshot_fields.html

equivalent of each of those fields.

That way the commission rates will be locked in and frozen at the time the detail record is created and they will not change retroactively. 

Excellent!!  Will give this a try.  Thanks for pointing me in the right direction.  

Took me a little bit to wrap my head around this, but finally got it. :)  At first, I was trying to make my lookup field a snapshot field.  I didn't realize that a snapshot field is an additional field.  
Thank You!

Good for you. This stuff is always easy in hindsight, but the very first time, you have to trip on your face a few times.