Hello! I need to move objects with greater precision; when I attempt to circle a word on a screenshot, the circle dances all around the word, but refuses to be smack in the middle of it. I assume this is because the rulers are only 1/8" increments. How can I adjust this? Thank you!

If you right click on a blank part of the slide, then click on grids and guides. Uncheck, snap objects to grid. Then when you create the shape it will not snap to 1/8" increments.

As Obbay2 says you can turn snap off. You can also hold down the ALT key while dragging objects to temporarily disable snap.

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i was kinda suprised that holding on the 'alt'-key when moving around my pictures didn't help placing them precisely anymore, in microsoft office professional 2010 .

so maybe this solution can help others as well:
1) right click on the picture so the tab "Picture tools - format" pops up on the top bar.
2) click on the tab "Picture tools - format" > then choose 'align' > then 'grid settings'
3) now uncheck the first box, which is called 'snap objects to other objects'

this did the trick for me. hope it helps others!