Usually a long press on the unit button. The part worth knowing is why some tools keep reverting to metric, and why one popular Bosch will not show you fractional inches in memory no matter what you do.
Almost every laser measure follows the same pattern, whatever the brand.
Find the button marked with a unit symbol, often shown as ft, m, or a small ruler icon. On compact tools it is frequently a secondary function rather than a dedicated button, which is why people cannot find it. Press and hold it for two to three seconds. The display cycles through the available formats each time you hold it again.
On units with a proper menu, units live in settings instead. Hold the power or menu button to enter settings, scroll to the unit entry, and select.
The setting applies to the live reading immediately. It does not always apply retroactively to measurements already in memory, which is the source of a lot of confusion covered below.
Most tools offer more options than people realise, and picking the right one saves conversion work later.
The one worth thinking about is decimal feet against feet and fractional inches. If you are calculating area or ordering material, decimal feet removes an entire class of arithmetic error. If you are cutting, fractional inches removes an entire class of measurement error. Set it to match what you are doing that day rather than leaving it on whatever it shipped with.
Two different causes, and they need different responses.
It resets after a battery change. Many tools store settings in volatile memory that clears when power is removed. This is normal behaviour rather than a fault, and the fix is simply to reset units and, importantly, to check the reference point at the same time, because that setting frequently resets alongside it and it matters far more.
It reverts on its own during use. This is not normal. It usually means the battery contacts are momentarily losing connection, which the tool experiences as a power cycle. Check for corrosion on the contacts and make sure the cells are seated firmly. Leica DISTO D1 owners report batteries that will not stay seated as their single most common complaint, and unexplained setting resets are one of the symptoms.
Worth flagging on its own because owners spend real time trying to fix it and it cannot be fixed.
On the Bosch GLM165-40, the memory function will not display fractional inches. Recall a stored measurement and it comes back in metric regardless of the unit setting on the live display. Owners have followed the manual, watched the available videos, and performed the hard reset through the pinhole, and it persists because it is how the firmware behaves rather than a configuration you have got wrong.
If you rely on stored measurements in fractional inches, this is a genuine reason to look at a different model. If you mostly read the live number and write it down, it will never affect you. It is a good example of a limitation that no specification sheet mentions and only owner reviews reveal.
Switching to fractional inches does not make the tool less precise, but it does change what you see. A tool measuring to a sixteenth will round its internal figure to the nearest sixteenth for display. Switch the same reading to millimetres and you may see a number that does not convert back exactly, because you are now seeing a finer slice of the same measurement.
That is a display artefact rather than an inconsistency. If you need the finest resolution the tool can give you, use millimetres or decimal inches. If you need a number you can transfer to a saw, use fractions. How much of that precision is real is a separate question, and the answer depends far more on how you hold the tool than on the units you display.
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