TDA2EG: 2D Surround View Calibration Checkered Pattern Size Issue

Part Number:TDA2EG

Hi

    I am calibrating the 2D surround view, and got a not bad geometric alignment result on the toy model car.

    Now i am trying to calibrate it on a real vehicle which is much bigger than toy model car.

    According to the "VisionSDK_UserGuide_2D_SurroundView_Demo.pdf", in the calibrating of toy model car, the print size of Checkered Pattern is A4. My question is that if i want to calibrate on a real vehicle, what the print size of checkered pattern should be? 

Thanks

xuanbo