Caesar Cypher - all letters work except 'z' - help please

[sjmgeezer]

Enter a letter to be decrypted in row AH1:BB1
The below rows provide every response possible for ‘Shift Register’ type cypher.

x REF = B2:AA2 > Find REF letter on this row
y REF = A3:A27 > Find REF number (AF2:AF26) on this column
Return x,y coordinate value > The shift Register modified value

To see it - add your name in the black 'Caesar Cypher cells.
All shift register responses are listed below - every other thing the text could be

‘z’ is the only letter that does not work - what have I missed?

Thanks

Caesar Cypher Table.ods

[mikekaganski]

OP uses a rectangular reference in INDEX, which has 25 rows per 26 columns; and passes there 26 (index of Z) as a row.

[ajlittoz]

What has this question to do with the mathematical formula editor (as is requested by tag math)? Please retag to replace math by calc. Type twice Enter to exit retag mode.

[PKG]

Index requests rows first and then columns, you have columns first and then rows.

INDEX(Reference [; Row [; Column [; Range]]]) 

16108695928979247.ods

[sjmgeezer]

Thanks so much - nice easy one - solved