Photoshop horizontal position of reference point

I have three images that I want to align. I have tried to set the x value of the horizontal position reference point, and Photoshop changes the value of one of my images by .5 px after every time I change it. The other two images will stay at the correct value, but the x value continues to change on the third image. I have tried toggling the relative positioning for reference point. Any suggestions would be greatly appreciated! Thanks!