What the Multimeter Reading Log does
This is a structured log for field measurements: point, quantity, the limit that applies, the reading and last round's value. It works out the deviation, flags anything outside limits or close to them, shows what has moved since the previous round, and exports the whole sheet as CSV or JSON.
The point of recording the limit next to the reading is that a number on its own is not a record. "241 V" means nothing in six months; "241 V against 230 V nominal, +-10%, was 238 V last month" means something. A row with no limit is marked as recorded rather than quietly counted as a pass.
Everything stays in your browser. Site readings are site records and are never uploaded.
How to use it
- Fill in the board or asset, who took the readings, the date and which meter was used - a reading without a meter reference cannot be defended later.
- Paste the readings as CSV, keeping the header row. It comes straight out of a spreadsheet, and the column names are flexible: Reading works as well as Measured, Nominal as well as Expected.
- Express each limit the way the job sheet does. Expected plus Tol% gives a band; Min and Max together give a window; Min alone means at least (insulation resistance); Max alone means no more than (loop impedance, leakage).
- Put last round's figure in the Previous column to get a trend. A reading inside limits that has moved 10% since last time is more interesting than one that has sat still at the edge of the band.
- Export CSV or JSON for the maintenance system, or print the sheet for the file.
Reading the results
Pass, marginal and fail are arithmetic against the limits you typed. Marginal means the reading is inside the band but using more than 80% of it - which your meter's own accuracy could easily close.
Recorded means there was no limit for that row. That is a legitimate state and is reported separately rather than being folded into the pass count.
Change is the difference from the previous round. Movement matters more than position: a busbar joint at 0.11 ohm rising to 0.18 ohm is still inside a 0.5 ohm limit and is still a joint that wants looking at.
The pass rate is calculated only over judged rows, so adding untested spare ways to the sheet does not flatter it.
Worked example: a distribution board round
Three phase voltages are logged against 230 V nominal with a +-10% limit, giving a band of 207 to 253 V.
L1-N reads 241 V: 11 V high, +4.78%, using 48% of the tolerance. Pass.
L2-N reads 255 V: 25 V high, +10.87%, 2 V outside the band. Fail - and it was 231 V last month, a 10.4% jump, which points at something changing upstream rather than a measurement error.
L3-N reads 252 V: inside the band by 1 V, but using 96% of the tolerance, so it is flagged marginal rather than called a clean pass.
The earth continuity row has no expected value, only a maximum of 0.5 ohm; 0.12 ohm passes. The insulation row has only a minimum of 1 Mohm; 550 Mohm passes, though it was 600 Mohm last time and that downward trend is the thing to watch.
The spare way has no limit at all, so it is recorded rather than judged, and the pass rate is worked out over the seven rows that had a limit rather than all eight.
Formulas and scoring rules
- Band from expected and tolerance
low = expected - |expected| x tol/100; high = expected + |expected| x tol/100- Deviation
deviation = measured - expected; percent = deviation / |expected| x 100- Tolerance used
used = |measured - expected| / ((high - low) / 2)Above 80% the row is marked marginal rather than a clean pass.- Change since the previous round
change = measured - previous; percent = change / |previous| x 100- Pass rate
pass rate = passes / rows that had both a limit and a readingRows with no limit or no reading are excluded, so they cannot inflate it.
Recording the meter, not just the reading
A reading is only as good as the instrument that produced it, and the first question anyone asks about a disputed measurement is which meter took it and when it was last calibrated. Recording the model and the calibration reference in the header costs nothing at the time and is the difference between a record and a note.
It also sets the floor for what a marginal verdict means. A handheld meter quoting 0.5% of reading plus two digits on AC volts contributes about 1.5 V at 250 V, so a reading 2 V outside a limit is not a comfortable failure - it is a reading that needs repeating with a better instrument.
Limits that are not bands
Much of what a technician measures has a one-sided limit. Insulation resistance must be at least something; earth fault loop impedance must be no more than something; leakage current must stay under a figure. Forcing those into an expected-value-plus-tolerance format invents a nominal that does not exist and produces meaningless deviation percentages.
This log keeps them as they are. A Min on its own means at least, a Max on its own means no more than, and the deviation columns stay empty because there is nothing to deviate from.
Limitations: what the result does not prove
- It does not include your meter's accuracy, its resolution, or the effect of test leads. Those sit underneath every verdict and matter most exactly where the verdict is marginal.
- It is a record of what you typed. It cannot tell whether the right point was measured, whether the circuit was live, or whether the meter was on the right range.
- A pass is not a test certificate. Electrical installation testing has its own forms, competence requirements and acceptance criteria, and they come from the standard that applies where the installation is.
- Trend detection compares two numbers. Two points is not a trend line, and a single previous reading cannot separate a genuine drift from a bad measurement last time.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- NIST Technical Note 1297 - Evaluating and expressing measurement uncertainty - checked 19 Sep 2026
- IEC 61010-1 - Safety requirements for electrical equipment for measurement, control and laboratory use
- IEC 60300-3-11 - Dependability management: reliability centred maintenance
Frequently asked questions
What should a multimeter reading log record?
The point, the quantity, the limit that applies, the reading with its unit, who took it, when, and with which meter. The limit is the part people leave out and the part that makes the log usable a year later, because nobody will remember what 241 V was supposed to be.
How do I log a reading that has no expected value?
Use the Min or Max column on its own. Insulation resistance takes a minimum, earth loop impedance and leakage current take a maximum. Leave the Expected and Tol% columns blank; the page then reports pass or fail against the one-sided limit and does not invent a deviation.
What does a marginal reading mean here?
The reading is inside the limits but has used more than 80% of the permitted band. It is a warning that the margin left is small enough for your meter's own accuracy, temperature, or one more round of drift to push it out.
Why does the pass rate not count every row?
Because rows without a limit cannot pass or fail anything. Counting them as passes would mean that adding untested spare ways to the sheet improved the result, which is the opposite of what a log is for.
Can I paste this straight from a spreadsheet?
Yes. Copy the range including the header row and paste it into the readings box. Tabs, commas and semicolons are all recognised, and the column names are matched loosely, so Reading, Measured and Value all mean the same column.
How do I spot a deteriorating connection?
Use the Previous column. A bolted joint or an earth connection rarely fails suddenly: its resistance creeps up over successive rounds while staying inside the limit. The change column shows that movement, and the page flags anything that has moved 5% or more even when it still passes.
Does this replace an electrical test certificate?
No. It is a working log. Certificates and condition reports have a prescribed form, prescribed acceptance criteria and a competent person's signature, none of which this page provides or replaces.
Are my readings uploaded anywhere?
No. The whole tool runs in your browser, nothing is sent to a server, and the CSV and JSON exports are generated locally in the tab. Closing the page loses the data, so export anything you need to keep.
Last reviewed by the A2Z.Tools team against the sources listed above.
