This is probably the engine offset. It varies from plane to plane depending on the planes design. It can be set up, down, left or right from a fraction of a degree to a number of degrees. Enjoy the assembly. You may want to reinforce the glue joints if you think they look weak. Make sure the hardware included is in good condition. Assemble and then triple check your balancing points and your radio set up. Make sure your batteries are correctly charged. Go to the field and have fun.