I have 4 columns in a grid. I need the value in the second column divided by the

Since the 3rd column is the denominator in the division, I would use an a!save() on the 3rd column. Something like: a!save(ri!costPerHour, quotient(ri!cost, ri!billableHours)), but you will want to null-check the cost and billableHours values before you try to perform the division.

I just realized you'll probably want to use the same a!save on both the 2nd and 3rd column, so that if either value is changed then the 4th column is updated.

Looks like this is a non SAIL form - you'd need to change to SAIL to be able to do the suggested. If you can't change to SAIL are you allowed to use javascript? You could try creating javascript rules for this. If not you could split the form into 2 one for entering the Cost and Billable Hours another that then shows the Cost per Hour with the ability to move back to the data entry screen if needed.

This is for version 7.3, we are upgrading to 7.8 but not in time for this project.

Since non-SAIL forms don't have the ability to dynamically update values, you'll to do this through a form submission. A solution for this case could be having a button at the bottom of the form saying "Calculate Hourly Costs", and using that button will submit the form, chain through a script task that calculates the hourly costs, and then chains back to the form.

To the end user it doesn't look like they left the form, and now the hourly costs are updated.

If you have 7.3 shouldn't you have the ability to do a SAIL form? Or does 7.3 predate editable grids?

If it is a normal grid (not paging grid), you can place JavaScript/Jquery functions as you need (on change, on blur events on 2nd,3rd columns)
1. you can use get value and set value methods to retrieve data from 2nd column, 3rd column by using fieldIds (like FormAPI.setvalue() and get value())
2. define variable by calculating both of them and set that value to the 4th column.
But here the crafty things is to get the index of that row from a dynamic grid view (adding/deleting rows).
If it is fixed set of rows, then just iterate the rows and calculate it using for loop.

I think the editable grids came in 7.5 - forum.appian.com/.../Appian_Release_Notes

I used
quotient(riCost,riBillableHours) saved as Cost per Hour

Thanks for your help, I never used the quotient function before.