The main entry correction is done for obstacles in front of the main door (dwar dosha), like a column, a tree, electric pole or any other obstruction, which cannot be removed. The main entry correction can also be done in general, as it helps in bringing positive energy inside.
Correction plate applied on the door frame. 2 on the corners and 1 in the center of the main door. South facing/West facing or any other dwar dosh (hurdle or negative energy in front of the main door). The Main door correction is applied to the door frame and hence throws back the negative energy to enter the inside environment and brings positive energy inside.