Self-referencing array function

Hi,

I am fairly new to VBA programming and I have got a question that is probably embarrassing simple to some:

I have got one range (lets call it "ARange") with double variables occupying the following area in my spreadsheet:
Sheets("Calc").Range("B3:CV3781")
And I want to calculate the cells in the following range (let's call it "BRange"):
Sheets("Output").Range("B3:CV3781")
using the following formula:
"=IF('Output'!RC="""",R[-1]C,R[-1]C+'Output'!RC)"

Is there an efficient way to get VBA to read what is in the ARange, calculate the BRange and post it as values without having to interacting with the cells in the BRange prior to posting the values?

My own attempts result in painfully slow code.