Shorter formulae makes file 3X larger

hi,
I don't know why the second formula triples the file size (although I suspect it may relate to the use of the array within the pinched brackets) but I do have some suggestions that may help bring it back down.

* Check the "last cell" on each sheet by using [ctl + end]. Ideally, this will result in the last row of data being selected (eg approximately row 2000). If the last cell is further down the sheet (eg row 10,000 or as extreme as 65K+) then you will be able to minimise the file size by deleting excess formatting (using the Edit-Delete option not "delete" on the keyboard which only "clears the contents").

thinking time...
1) This option decreases the number of calculations completed for each cell by splitting out the duplicated equation.
Put the below in a blank column (eg col G):
=MID(F11,4,1)
& put the below into the next column (eg column H)
=IF(F11="","",IF(G11=""," ",IF(OR(G11={"1","2","3","4","5","6","7"," "}),G11,"ERR")))

2) Similar but removes the use of an array - relies on G12 being able to be interpreted as a number.
Put the below in a blank column (eg col G):
=MID(F12,4,1)
& put the below into the next column (eg column H)
=IF(F12="","",IF(G12=""," ",IF(OR(AND(G12>0,G12<8),G12=" "),G12,"ERR")))

or maybe
=IF(F12="","",IF(G12=""," ",IF(OR(AND(value(G12)>0,value(G12)<8),G12=" "),G12,"ERR")))

Also, I suggest changing the results for "" or " " to a brief phrase (depends on what the result is used for) because as it is currently written users can't differentiate between "" & " ", can they?

I don't know if these suggestions will help but I hope they do.

Rob