If a scale is not mounted on a level surface, that scale cannot accurately measure the weight of an object placed on it.
What can that scale measure? A scale measures the force exerted perpendicular to its surface. Push down on a scale, and the display will show the force placed on it. [More precisely, it’s trying to show a mass measurement…but let’s avoid the mass/weight clarification for now.] Push at an angle, and the scale will still only show the component of the push in the direction the scale can measure.
When we weigh an object, we are measuring the force that the Earth’s gravity is exerting on that object. Gravity always points in one direction – towards the center of the Earth. For an accurate measurement from the scale, the force of gravity (just like the push from your hand) must be perpendicular to the surface of the scale. If not, then the scale is only measuring part of the true force of gravity.
This can be easily observed. Find a level surface, place your scale on it, and then place an object on the scale. Shim one side of the scale (a bigger angle will have a more dramatic effect). The scale will read as if weight has been removed – but of course gravity is still acting the same!
For best results with the acaia scale, use a level surface. If needed, however, the scale can rest on uneven surfaces and still have close-to-accurate readouts.
Acaia University is a blog post series where we share our scale research and strive to educate the broader coffee community.