# Accelerometer output value across the globe

Hi,
So… I have this random question that only a person like me would ask.
Ok, so say I’m here in north America using my 328PB with an accelerometer
on a surface i would consider flat and generating these values and on…

`````` X = 0.0220
Y = -0.0080
Z = 1.0418

Accelerometer:
X = 0.0190
Y = -0.0040
Z = 1.0318

Accelerometer:
X = 0.0230
Y = -0.0070
Z = 1.0298

Accelerometer:
X = 0.0210
Y = -0.0080
Z = 1.0298
``````

My board is sitting on a flat surface and nothing is moving
and as you can see the values being generated aren’t changing that much.
So my question is that say i’m to go to new Zealand or China with my board
and then, again, on a flat surface, run this experiment again, what are the odds of
the results being the same ?? As in are the values generated going to be pretty
similar with some small ± deviations or are the values going to be completely different ??

Hello.

The strength of gravity does change at different points on Earth’s surface, but the magnitude of that variance is very small. So, whether you can measure that depends on your specific accelerometer, but I suspect it would be impractical to use accelerometers like the ones we carry for that purpose.

As another reference point, this article makes it seem like characterizing that type of gravity variance is an ongoing project that organizations like NASA use satellites for. That article is pretty old and discusses a now completed mission, but it seems like there is an active follow up mission discussed here.

- Patrick

The variation in output you see is probably normal sensor noise. The sensor data sheet will tell you what to expect, although the data sheet may be a bit difficult to interpret as the values depend on the filtering.

You can reduce the noise by averaging many samples, e.g. averaging 100 samples reduces the sensor noise by a factor of 10.

The sensor output also depends strongly on temperature, so temperature variations must be reduced as much as possible.

To detect the slight variations in the pull of gravity at sea level, in various places around the world, you would definitely need extensive averaging, and account for temperature variations.