How do I known if the front frame rails are bent

The checking of the frame rails for accident damage can be done easily. First place the vehicle over a flat clean cement floor. Select points on the frame rails such as front ends---suspension points---brackets attached to the rails on both sides and rear ends of rail. Make sure the points selected have a corresponding point on the other rail. Using a plumb bob drop the selected point to the floor and make a cross on the floor at that point. . Repeat the process for each selected point. The more points the easier to find where the rails are bent and by how much. Move the car out of the way and using a tape measure the distance diagonally between same points.-- EI-- from left hand front end to right hand rear end. Repeat the measuring from the opposite corners By measuring from one point on one side to the second point on the other side you will develop a continually crossing pattern of measurements. So in the end if you selected 4 points per side you will have 3 sets diagonal measurements on the floor or more . As you measure write the dimension on the floor. Now if there is a difference of more than 1/4 "(6mm)between any set of diagonals you will see if the rails are bent and if they are bent right or left or bowed in the middle. By measuring the heights of the corresponding points and recording them you will see if the rails are bent up or down. I understand it is a bit long winded but you will be in effect transposing the measurements of the points of the rails onto the floor so that the differences can be measured without the problems of items interfering with straight line distances.