How do animators draw graphics at same place in each frame?

Question

Take the example of older days when computer graphics didn't exist like Tom and jerry in 50s or hand drawn animation in Paper Flipbook in modern times .see https://img-9gag-fun.9cache.com/photo/aV3M8NK_460sv.mp4 for example How are animators able to draw the same image in same proportions at same spot over several frames almost flawlessly?clearly without any aid its not possible to draw the same object on each frame at same place and with correct size and color as the last frame.how do they accomplish this?

Answer 1

Before computer software provided things like layers and onion skinning animation was drawn on sheets of acetate that were clear cels with holes punched in them to keep things registered properly. Animators also use light tables to see their previous drawings. Here are some images of animation drawing desks.

https://chrismcdonnellanimation.wordpress.com/tools-of-the-trade-2/

Answer 2

 By taking advantage of 1}the "onion skin" feature allowing a faint image of the previous screen to appear on the new frame screen or 2) duplicating the screen, making adjustments and save it as the next screen in numerical order