The space is the Intersection operator, which returns a reference to the cells common to the ranges in the formula. In the example below, cell C7 is found in both ranges, so it is the intersection.
=B7:D7 C6:C8
See:
Technique 2 – Using Named Ranges & Intersection (SPACE) Operator
here: http://chandoo.org/wp/2010/11/09/2way-lookup-formulas/
TPlacing a space between two references will return only the cells that intersect those ranges. This concept is easier to understand with a different example.
=SUM(A:A 2:3)
This formula has 2 ranges: A:A and 2:3. The intersection of these is A2:A3. The SUM would then return the value of A2 + A3. Now, what if we left off the SUM function, like so?
=A:A 2:2
The intersection of these two ranges is a single cell, A2, so the formula will still work. This last one is a pretty close example to what you had. Each of the INDIRECT functions is generating a range, and the overall formula then will look at the intersection of those two ranges.
See:
Technique 2 – Using Named Ranges & Intersection (SPACE) Operator
here: http://chandoo.org/wp/2010/11/09/2way-lookup-formulas/
Placing a space between two references will return only the cells that intersect those ranges. This concept is easier to understand with a different example.
=SUM(A:A 2:3)
This formula has 2 ranges: A:A and 2:3. The intersection of these is A2:A3. The SUM would then return the value of A2 + A3. Now, what if we left off the SUM function, like so?
=A:A 2:2
The intersection of these two ranges is a single cell, A2, so the formula will still work. This last one is a pretty close example to what you had. Each of the INDIRECT functions is generating a range, and the overall formula then will look at the intersection of those two ranges.