I am REALLY confused about X/Y/Z delta movement blocks

I am trying to use delta movement blocks to find out if an entity is moving or not. I've been looking through the internet for almost 2 days now and only thing I could have found was that you may be able to say when an entity moves by seeing its velocity values and velocity values are renamed to delta movements. But its always shows 0 when Im on the ground even if I'm moving and only changes when I jump.

This is really necessary for my mod so thanks a lot if you can help me. Thanks a lot anyway if you read this but couldn't found a solution.