I try to highlight a bar graph (exported from Excel) by adding an arrow at the tip and the bottom of a specific bar but it drives me nuts, that the grid at which Powerpoint orients itself results in the arrow not being exactly in the middle of the bar. Moving the whole bar graph doesn't bring a solution to this. Can I just move the arrows freely?
Hold down the ALT key while you move the shape with the mouse; that'll temporarily disable snapping to grid.
Or right click off the slide, choose Grid & Guides and turn off Snap To Grid in the resulting dialog box.