LOG returns the base-10 logarithm of one positive number: =LOG(1000) has the expected result 3, because 10³ = 1000. It answers “what power of ten produces this value?” Calligra’s documented form takes one argument, unlike Excel’s optional custom-base LOG.

=LOG(x)

• x (required): a positive numeric expression, constant, or reference. The handbook specifies a floating-point input greater than zero.
• Base: fixed at 10; there is no documented second base argument or default argument in Calligra’s LOG(x) signature. For a custom base, use LOGN(value;base); for base two, LOG2(x).
• Return: floating-point common logarithm; outputs can be negative when 0 < x < 1, even though the input cannot be zero or negative.
• Documentation edge case: KDE explicitly says LOG(0) is an error. We did not run Calligra to identify the exact UI error display.

This guide is release-scoped to Calligra Sheets 26.08.2 (KDE’s release listing dated 2026-10-08). The function is present both in the official stable-KF6 function handbook and in KDE’s pinned 26.08.2 source-function registry; references were accessed 2026-10-11. The handbook’s surrounding revision may be older than the release: source registration documents that a name is available in that release’s code, not that it was executed or enabled in a particular Linux package or other platform. Calligra recommends Linux packages/Flatpak; installed versions and optional components can differ.

In a cell, start a formula with =. The KDE English documentation uses semicolon (;) as the multiple-argument separator; the examples use periods for decimal points. Actual entry conventions may vary with locale or build. Use the installed function selector to confirm locally and keep input columns numeric, not numeric-looking text. Results are floating-point values; displayed precision is controlled by cell formatting. All results below are expected mathematical values, not observed Calligra 26.08.2 outputs.

1. In A1 type Positive value; in B1 type Common logarithm.
2. Enter the numeric values listed in A2:A6. Do not put a leading apostrophe before a numeric input.
3. Enter =LOG(A2) in B2 and fill it down to B6.
4. Set column B to three decimal places and compare the result with the table. The log is an exponent, not a ratio or percentage.

Sanity checks: For a positive A2, =10^LOG(A2) mathematically reconstructs A2, up to floating-point rounding. Two quantities differing by a factor of ten differ by exactly one common-log unit mathematically.

For an idealized dilute aqueous solution, the usual textbook approximation is pH ≈ −log₁₀([H⁺]) if the concentration is expressed numerically in mol/L. Real pH depends on hydrogen-ion activity, temperature and chemical conditions; do not treat a concentration-only estimate as a calibrated measurement.

• Put a positive hydrogen-ion concentration, for example 0.00001, in D2.
• In E2 enter =-LOG(D2); the expected numerical answer is 5.
• If D3 is 0.0000001, E3’s expected value is 7. A tenfold lower concentration raises the textbook pH estimate by 1.
• To avoid invoking LOG on a zero/negative input, guard values using the documented IF function: =IF(D2>0;-LOG(D2);"Check concentration"). This check is only for positivity; it does not validate chemistry or confirm text-cell coercion.

For pure mathematical scaling rather than chemistry, the same operation LOG(new/old) describes the number of tenfold changes, provided both quantities are positive and measured in the same units.

• Zero or negative input: no finite real base-10 log exists. KDE specifically documents zero as an error. A negative input is outside the function’s stated positive domain; the precise UI error code for it was not tested.
• Input between 0 and 1: a negative output is correct, not a failure. LOG(0.1) is −1.
• Two arguments copied from Excel: LOG(8;2) is not Calligra’s documented LOG syntax. Use LOGN(8;2) instead for base 2.
• #VALUE! or other error: verify that inputs are numeric, punctuation follows the installed locale and formula syntax is entered with an initial =. Do not assume an identical error code in every Calligra build.
• Scientific notation: 1E-5 represents a positive number; log calculations can be sensitive to an imported string "1E-5" that was not recognized as numeric.
• Rounding: LOG(0.8) should be about −0.096910013; limited cell display precision can conceal small discrepancies.
• Unexpected workbook conversion: confirm the argument count and base when importing LOG formulas from Excel or Calc, rather than assuming compatibility.

Excel documents LOG(number,[base]) with an optional base that defaults to 10; LibreOffice Calc similarly documents LOG(Number [; Base]). Calligra’s LOG(x) has one argument and is explicitly base 10. Consequently, LOG(100) agrees across the programs in its mathematical intent, but LOG(8,2) from English-locale Excel requires conversion to Calligra’s LOGN(8;2) or LOG2(8). Excel and Calc also have LOG10(number) for the fixed-base case. This is documentation comparison, not an actual cross-application workbook test.

• Calligra Sheets — function documentation
• official stable-KF6 function handbook
• KDE Calligra 26.08.2 source registration
• LibreOffice Calc mathematical functions

Verification status: Official documentation checked; example outcomes were independently reasoned or arithmetically checked where applicable. Not executed in Calligra Sheets.

• No genuine Calligra Sheets screenshots are included; this guide does not use mock application images.