After years of going without a tire pressure gauge I finally decided to buy one last night. I used it as soon as I got home on my cold tires (car been sitting in the garage since sunday) and to my amazement my tires are shy of about 2-3psi or air.

My question is, when i drive my car to the gas station to put some air in the tires, should I first take the pressure of the tires and then fill them by 2-3 psi more than what the gauge is reading? or should i just fill the tires until they are at 30 psi, which is what Honda recommends, not knowing if the pressure has increased or decreased as I drove.