SCP1000 pressure sensor reads a drop in pressure

I have an SCP1000 that I am trying to use as an altimeter. The desk I am at has a shelf that is about 22 inches higher than the main surface. When I move the altimeter from the main surface to the shelf it reads an increase in pressure, whereas I would expect a decrease. Also while I am moving it, it initially reads a drop in pressure but then goes up. Is this normal or does anyone know what might be causing this.

In addition, the datasheet says that I should expect values at least 12000, but I am getting values around 10000, is this an issue or not something to worry about?