Indirect Named Range Different Sheet

Explanation

The formula above evaluates something like this:

=SUM(INDIRECT("'"&B6&"'!"&C6))
=SUM(INDIRECT("'"&"Sheet1"&"'!"&"data"))
=SUM('Sheet1'!data)

Once the string is assembled using values in B6 and C6, INDIRECT evaluates and transforms the string into a proper reference.

Note you can refer to a named range in a formula without using INDIRECT. For example, the formula in D6 could be written:

=SUM('Sheet1'!data)

However, if you want to assemble the reference as text, and have Excel treat the text as a reference, you need to use INDIRECT.

Note: The single quotes are added in the formula above so that the formula will work when a sheet name contains spaces.

Explanation

The INDIRECT function tries to evaluate text as a valid reference. In this case, the sheet name is pulled from column B and concatenated with an exclamation point and the text A1:

=B5&"!A1"
="Sheet1"&"!A1"
="Sheet1!A1"

The INDIRECT function then coerces the text “Sheet1!A1” into a valid reference, which is passed into the SHEET function.

The SHEET function then returns the current index for each sheet as listed.