user10673: I have an animation in After Effects where I am animating a slider to move up and down at certain points. The slider should be mainly stationary, but moves occasionally in line with other actions on the project.

What I am finding though, is the slider is moving a small amount even when the keyframes are set such that it should be static. E.g. the following two keyframes are the same (Y position = 524.6) but if I move the marker in between, you'll see the value deviates from this. (As a result the slider moves.)
1st Keyframe (Y Position = 524.6):

2nd Keyframe (Y Position = 524.6):

In between (Y position varies, up to 525.4):

This is driving me nuts! As far as I can see the anchor point does not move, so I don't understand why this should happen.

user4426: It's because of spatial interpolation.  Here's a previous answer:
Object moving to a position I didn't specify

10673: <p>I have an animation in After Effects where I am animating a slider to move up and down at certain points. The slider should be mainly stationary, but moves occasionally in line with other actions on the project.</p>

<p><img src="https://i.stack.imgur.com/sK56t.png" alt="enter image description here"></p>

<p>What I am finding though, is the slider is moving a small amount even when the keyframes are set such that it should be static. E.g. the following two keyframes are the same (Y position = 524.6) but if I move the marker in between, you'll see the value deviates from this. (As a result the slider moves.)</p>

<p>1st Keyframe (Y Position = 524.6):
<img src="https://i.stack.imgur.com/yZrVb.png" alt="1st Keyframe"></p>

<p>2nd Keyframe (Y Position = 524.6):
<img src="https://i.stack.imgur.com/5EJFt.png" alt="2nd Keyframe"></p>

<p>In between (Y position varies, up to 525.4):
<img src="https://i.stack.imgur.com/ihVtB.png" alt="In between"></p>

<p>This is driving me nuts! As far as I can see the anchor point does not move, so I don't understand why this should happen.</p>
 4426: <p>It's because of spatial interpolation.  Here's a previous answer:</p>

<p><a href="https://video.stackexchange.com/questions/14687/object-moving-to-a-position-i-didnt-specify/14697#14697">Object moving to a position I didn&#39;t specify</a></p>
