Do I add a degree when taking underarm temp with digital thermometer?

[harleysmammy]

3 days ago we had to go to out of hours because my 4 week old son wasn't feeding properly. He had a temperature (done with a forehead strip) and cooled right down when stripped off so I think it was just warm. The doctor said to buy a digital underarm thermometer as the forehead strips aren't any good. So I bought a Braun digital one and it's showing up green at 36.8. I've just read you have to add a degree for under the arm, so do I need to even with a digital? One that cost me £16 haha. And even if I do need to add a degree, 37.8 is good right? He's not acting at all feverish, not too warm to touch his chest and he's acting normal and feeding okay again, I just want to keep a check (bit paranoid).
Thanks x