I am following a tutorial on using the slide constraint, and it says that there is a little blue ball in the middle of it to define the axis, but I don't seem to have one. The tutorial is here:

http://www.youtube.com/watch?v=ZStp7kGi ... dded#at=31
Not quite sure how to fix this, or how to define the axis without it, and all my attempts to set the axis manually seem to result in the entity I constrain vanishing. Not quite sure what is happening to it. Any assistance would be appreciated.
Thank you,
Sound Logic

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The little blue ball is there because of 'helpers' being turned on. On the menu to the top-right there is a wireframe-looking sphere which can turn helpers on or off.

Thank you, that fixed it.
Also: Is there anyway to make two objects be constrained in only one dimension? I'm trying a combination of sliders and springs, but it isn't working. Is there anyway to keep objects at the same position on a given axis?
Thank You,
Sound Logic