One centimetre here and there is really not inconsequential, use an electric measuring tool to be safe. No need to look for a power outlet, since it runs on batteries. Just get at it!
From ManoMano
Bosch - gpl 5G aa batteries Point laser
Powertool World
Bosch Professional GPL 5 Self-Levelling 5 Point Laser Measuring Tool 0601066200
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