problem cropping images in Pages

When I drag an image into Pages, double-click on the image, and use the Crop feature by dragging the edge of the image, I am sometimes unable to choose the exact size of the image that I want. The crop line jumps farther than I want to go, and won't settle on the size I desire. For example, I might want the image to be 1.56 inches wide, but no matter how slowly and carefully I drag the crop line, it suddenly jumps from 1.63 to 1.52 inches.

Is there a solution to this? I thought perhaps the left or right arrows could be used...

Thanks for any help.