Brinnie's Christmas Box

I have placed my Christmas Box somewhere on Dartmoor. You will have to find Pole 29 and go 2 paces on 290 deg. To find the pole you will have to crack the code.

888844444444777777788888888899999

This converts to a 10 figure OS reference. You don’t need to have GPS to get this box.

Good Luck

I forgot to mention, please do not give any clue to where the box is, in your replies.
Many thanks
Brinnie

can i have a clue as to how to crack the code, i think the sherry is getting to me!