Instruction: Answer the given question by extracting information from the supporting document.

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Question: Can the mount be set up to move horizontally in everyday use or is it a one time setup with lock screws.
Document: Well made, solid, easy to put together and mount - the instructions are a little lacking. I have a 40 in. space between 2 windows and wanted to mount a 39.5 in. TV exactly between them - I had off center studs so I really needed a mount that could slide left to right to perfectly center the tv. I actually ended up having to shift the mount all the way over to one side and could only use 1 set up screw holes instead of the 2 provided. But the TV is relatively light (under 25 lbs) and the mount and the screws etc., are solid enough that I have no worries about the tv coming down.
Looks and works great. Easy setup and instructions. High quality. But Amazon description says up to 55 inch TVs supported while the box and instructions upon delivery say 50 inch.Note, for newer Samsung 55 inch EH6070/6000 series owners. These TV's require M8 15mm to 17MM mounting bolts. Smaller TVs use M6 to mount the bracket to the TV. So this mount will be delivered without the extra four M8 bolts you need.One set of 4 M8 15mm bolts is included with this TV mount. However, if you use those to mount the bracket to the TV, there is nothing left to mount the bracket to the mount which also requires M8 bolts.
Only reason I don't give it 5 stars is because set up was difficult. Be careful if you need to remove the mounting bars (you have to if your TV's mounting holes are 8&#34; apart), one of the screws was so tight that it stripped and I ended  up having to buy a screw extractor at home depot. Then  to mount, you have to hook the TV and attached back plate with exposed screws to a very small area on the mount (hard to explain but you'll see from the manual).
I completed mine with the help of my 15 year old son, and helped out for about 2 minutes of the install-  It took much longer, but I only needed a second person to assist when it was time to mount the first bolts to the studs in my wall. Other than that, if you're a healthy, strong adult, the rest can be a one man job.
I put a new Visio 42 inch tv on this wall mount. It works great. There is 25 inches of extension and the tv swings a full 180 degrees.You can move the tv 4 feet across the wall.This puts the TV in the center of the room or 4 feet over to be in front of a treadmill.The large back plate installs over 2 wall studs. The center pivot point can be moved any where between the studs, in 2 inch increments. My setup ended up with the pivot point directly over the stud.
Nice piece. Very heavy duty.If you own the "very rare" Samsung LCD (They only made a few hundred of these, right?) the kit will not include the screws required when you use the standoff bushings. Luckily I had a few of these when I mounted another TV in the bedroom.Otherwise, the mount is great. The plate that screws onto the wall is a brute.I was confused by the directions when they stated to "Make the TV level, simply twist". Son of a gun.
None were needed for the Visio.The tv with the mount attached is simply set on the swing arm and 2 more screws permanently affix it. Again the TV was the lightest part of the assembly.The Cable management is just adequate but a few Zip ties improved what was lacking.I am exceedingly pleased with this unit. I would recommend it to anyone who can mark studs and drill a few holes.I compared it to a $300 version sold at Best Buy. This mount is twice as sturdy, the pivot point is adjustable on the wall, and it is 1/3 the price.Did I mention that it was sturdy?
Nice solid construction heavy duty. Instructions need to be more specific in what screws to use where, but figured it out. Like the sliding feature on the base. Also the leveling feature is nice once mounted If.its not perfect, you can lift the end to level tv. Not sure if I got the tilt working or if what I am doing is 15 degrees, but overall nice product
Then the swing arm is installed by just sliding it into the wall mount. The wall mount holds the bracket during adjustment. 4 screws permanently attach the swing arm to the wall mount. This is easily done by one person. The swing arm moves smoothly and solidly with or without the TV mounted.The tv mounting seams very versatile with numerous mounting arrangements. The Visio did not need either the horizontal or vertical extension bars, so neither were installed. Holes aligned perfectly. A couple of different length screws and some spacers were included just in case.
Terrific product- Well constructed, solid, and when installed-  you'll be able to move your 50&#34; LED screen around like it's a light weight monitor. The difficult parts of installing the product are not design related, this is a very well designed product. It's simply that it's heavy, and your LED Screen (if you're buying this model) is awkwardly shaped for completing a one person install. The very nature of installing a heavy duty (strong) articulating TV arm to studs in your wall is really a two guy job.
Answer: The mount will move horizontally.  I have not needed to lock mine into a fixed horizontal position so it will move if I push on the left or right side of the tv.