I have just touched off my part and it is saying it is +1.3mm.
Visually it looks like the bit is further down than it should be so I think it confirms that it is slipping.

I am using the correct collette size and it is tight when I insert the bit.
Not stupid tiht but it grabs onto the bit.
I am not over cranking the thread when putting it onto my spindle as I don't want to over do it. But it is still quite tight.

What is my best option here?