Work with the example
Did K1 really record zero, or is its reading missing? A contains unique keys; B5 is numeric 0, B6 is a true blank and B7 is 7. G5 starts at K1. H5 finds its row; I5 checks the matched cell rather than trusting a zero-looking raw result.
| Key | Reading cell | Checked output |
|---|---|---|
| K0 | Numeric 0 | 0 |
| K1 | True blank | Reading missing |
| K2 | Numeric 7 | 7 |
Edit the working cells
H5 uses MATCH with exact 0. I5 first propagates an ISNA(H5) lookup error; then ISBLANK(INDEX(B5:B7;H5)) detects the true blank. ISNUMBER accepts a numeric reading and refuses other types. Change G5 to K0: I5 returns 0. A fresh B6 formula ="" or text "0", with K1 selected, gives Reading not numeric. K9 retains #N/A.
Check the failure case
J5’s raw INDEX shows 0 when K1 points to the true blank in Calc. Reporting that zero invents a reading. A formula-empty cell is also different from a true blank, and a text zero remains nonnumeric.
Why is numeric 0 accepted but text "0" refused?
Show the worked answer
The exercise requires a numeric reading; a visible glyph alone does not establish the stored cell type.