ONLYOFFICE #NUM!: Check Numeric Domain Before Changing the Formula

Scope: ONLYOFFICE Spreadsheet Editor English function documentation checked October 21, 2026. The help pages are not pinned to an installed build. Record whether you use free Desktop Editors or a hosted editor, its version and platform; these examples do not certify older builds, mobile editions or desktop/server parity. No application was executed for this reference. Use a disposable workbook; expected results are documentation-based checks, not native observations.

Inspect the input immediately before the failing function

ONLYOFFICE’s SQRT documentation explicitly says a negative argument produces #NUM!. A cell can contain a genuine number and still violate a function’s requirements. Number formatting does not make an invalid argument valid.

Start by copying the inner arithmetic into a spare diagnostic cell in a test copy. For example, if the formula is =SQRT(B2*C2), examine B2, C2 and their product separately. Do not change the outer function until the sign and units of those components make sense.

Reproduce and repair a signed-input mistake

In a new sheet, enter -4 in B2 and 9 in C2. Enter =B2*C2 in D2 and =SQRT(D2) in E2. D2 should be -36 and E2 should show #NUM!.

For this exercise, assume B2 represents a positive measured length and the minus sign was a transcription error. Replace B2 with 4. D2 should become 36, E2 6. Then change C2 to 16 and verify D2 64, E2 8. Set B2 to 0 and verify both results are 0. Restore B2 to -4 to confirm the deliberately invalid input is still exposed.

The correction is legitimate only because the exercise defines B2 as a positive measurement. In a real model, a negative quantity could be meaningful. Establish the data definition and verify the source before changing its sign.

Different functions have different boundaries

Do not turn the square-root rule into “zero is always valid.” The official LN reference requires a number greater than zero. Thus zero passes the square-root boundary but fails LN’s documented input requirement. This page does not assign an unverified displayed label to LN’s invalid-input cases.

A useful valid control is =LN(1), whose expected result is 0. Read the specific function’s documentation for its domain and any other constraints before interpreting a different #NUM! occurrence. A statistical or financial calculation may involve requirements beyond the sign of one cell.

Avoid cosmetic repairs

Adding ABS, replacing negatives with zero or wrapping the result in IFERROR can make a sheet look clean while changing its meaning. None of those actions proves that the original quantity was appropriate. For example, the real square root of 36 is 6; applying ABS to -36 silently substitutes a different input.

If negative values are legitimate, reconsider whether the model should use this real-valued transformation. If they are data errors, correct them from evidence and retain an audit note. If they are unavailable data, preserve that status rather than inventing a number.

Verify an ordinary positive case, the applicable boundary and an intentionally invalid case before accepting the repair. Use the SQRT guide, LN guide and error selector to continue. The general troubleshooting reference covers build, import and calculation context.