This water treatment stuff if CONFUSING!

Can someone give me a bit of reassurance that I am going to do this right?
I have got a tub of DLS from my local HBS and am planning on using some tonight.
So here goes:
(I believe mg/l is the same as P.p.m.)Yorkshire water quote:
"Water hardness average: 36.3mg/l calcium"
So I need another 140(ish) p.p.m's of Calcium.Brupack quote:
"A typical Bitter requires a calcium content of 180-220 p.p.m."
Which from Brupacks table is 0.8grams / litre of DLS.
Assuming I use 10litres of mash water I should add 8grams of DLS to my dry grain. Am I right?

I already use camden tablets to remove chlorine.
Will this suffice for a first stab?
Cheers,
Neil