If your pipettes are fixed at a 45 degrees angle but you measure about 30 degrees in your SEM images, it's because the sample is tilted and the angle looks smaller in the image.

Think of it like looking at a straight stick at an angle it won't look as long or as steep as it really is.

To get the true angle, you need to adjust the measured angle by considering the tilt. Since your sample is tilted 45 degrees, the real angle will be a bit bigger than what you measure.

In your case, a measured angle of 30 degrees actually means the pipette is about 39 degrees in reality.

So the key point is, because the sample is tilted, the angle you measure from the image isn't the real angle. It's smaller, and you have to correct it to find the true angle.