And in the likely manufactured soft ground, I'll be allowing two lengths per pound in my calculations.
Sometimes, if quite a few of the previous running's horses are going again, I map them out on a piece of paper with a ruler using a cm per pound and then converting each cm to two lengths.
For example, I'll make a mark to represent the winning post about 2/3 way along the page and that will represent that previous year's winner on my figures. I'll then map the others to the left of it on the lower side of the line.
Then I'll map this year's rating difference (not weight) above the line.
So I A Maximus will appear at the mark underneath the line (cos he won) but since he is 8 higher in the ratings I'll map him 8 cm to the left of that above the line. Delta Work is no longer with us. Minella Indo (3rd) beaten 8 lengths, will be 4cm from IAM under the line but is a pound lower so will be 1cm to the right above the line. Galvin will be next to MI below the line and above it since he too is a pound lower. Coko Beach, though will be just over 16cm to the left of IAM under the line but he is 11lbs lower so will map 11cm to the right of that above the line, 3cm in front of IAM. So in theory CB should finish six lengths in front of IAM at the revised weights (19lbs for 33 lengths).
The question is, how liely is that to work out in practice. For me, IAM was getting better the further they went, is a year more mature and very probably better so could confirm his superiority but CB got messed about in running and maybe we didn't see the best of him. All part of the fun of the National. IAM is currently 14/1 and CB is 100/1 so I know which I want to be on at this stage.
But all that only relates to last year's runners who are running again.
There will be other runners who are better handicapped this year than IAM was last year. They are the ones I want to be on.
Edit - One such type might be Hewick who went up to 169 for winning the King George the season before last but gets in here off 161. He's 66/1. My concern with him is the likely manufactured soft ground as he really needs it good so I don't really want to back him until somebody goes NRNB.