Calculation of Material Takeoff for Internal Plaster to wall surface

[geteway2digitalindia]

I defined Wall N1 as a 210mm th wall having 200mm th brick + 10mm th Internal Plaster.

Area of internal plaster should work out to 10 x 4  = 40 sqmtrs

But Material Takeoff sheet showing 41.60 sqmtrs.

Not getting this difference

[mhiserZFHXS]

Change the wall join.