Here's another explanation that I found easier to understand from a VERY well-respected technician...


3rd axis adjustability on a sight,
just means that the scope housing has a door hinge on it.

It allows you to swing the door away from you,
or it allows you to swing the door towards you.

Here is an experiment.

Grab a 24-inch carpenter's level in your right hand.
Hold you right arm level (parallel to the floor).

Now, pretend the carpenter's level is like a door,
and while keeping the bubble level parallel to the floor,
swing the left end of the bubble level towards you
so the bubble level makes a 45 degree angle with your arm.

If you look at the bubble on the level, the bubble is still in the middle.
The bubble level frame is at 45 degrees to your arm, not even close to being 90 degrees.

Now, raise your right arm.

Look at the bubble.

The bubble is now all the way to one side.
If you tilt the bubble level,
and make one end of the frame lower, much much lower,
then you can make the bubble appear in the middle.


That's why, if you happen to BUMP your pin guard,
or your scope housing,
and you change the DOOR SWING ANGLE
to something more or less than 90 DEGREES,

then on a long range shot (80 yard field shot),
or a uphill shot (say a 3D target)
or a downhill shot (say a treestand),

the bubble will lie to you,
and force you to tilt your bow to one side,
to force the bubble into the middle

and you are going to miss a little to the left or a little to the right.