Could someone clarify the trolley jack vs. floor jack difference a bit more? The one that I bought from Harbor Freight does pull things back towards the user a bit as you reach full extension, but I always thought that was the nature of the beast. The link that Off-Roader posted looks just like mine but seems to have an extra small "arm" that runs up alongside the main lift arm that mine does not have. How does the floor jack differ that allows it to lift vertically? Learn something new every day...