The accuracy of a 3D scanner really depends on the device itself. And generally, the more expensive the more accurate the results. Most of the scanners we reviewed have adequate accuracy for their target user-base. They carry out both a 3D structure scan and texture scan of an item, along with its color. This is done via either several 360-degree scans on a rotating plate at different angles or by the user themselves if using a handheld scanner.
3D scanner accuracy is measured in millimeters and is sometimes called spatial accuracy or special resolution. A good range is considered between 0.5mm and 0.001mm. The smaller the number the better - this measurement refers to how close the scanned model is to the original. I.e. inaccuracies lead to incorrect sizes. An extremely bad scan would produce a blurry blob that could end up several millimeters bigger than the original.
Like regular photos and videos, resolution can also play a role in accuracy and detail. Where accuracy is the parent measurement of how correct the scan is overall, when compared to the original, resolution refers to the distance between each scanned point of the object. The higher the resolution the less blurry the surface of the model will be. Think how low-resolution images look pixelated, though not necessarily inaccurate.
Many software programs that come with scanners allow you to set the resolution upon saving the model. A particularly high resolution can take up computer resources and may not necessarily result in much difference when 3D printed if the object itself is not that complex, to begin with.
Regardless of accuracy and resolution, most devices have trouble with 3D scan textures when it comes to hair because it has such fine detail.