Setting the timing on a LR90 2.5 petrol - pully markings

[mlambton]

Can anyone help me understand the pully wheel markings on my new 1986 LR 2.5 petrol.

I wanted to set the timing today at the recommended 15 BTDC. But when I look at the markings on the pully wheel it showsa number of graduations but has 6 degrees stamped at either end of the graduations - I cant work out where the setting point is

thanks for any guidance

Mark