a.s.arghmatey - I think what Jester is saying is that he prefers to increment in kgs rather than based on a %, it just so happens with his examples that the figure is around 2.5% (if he had chosen 150kgs and added 5kgs that would have been 3.33%). If you achieve your 5 rm you would then increase the load by either 2.5 kgs, 5 kgs or even 10 kgs depending on which body part etc, say your best for 5 rm on flat bench is 120 kgs and you would generally increase this by 2.5 kgs on your next workout then increment backwards by 2.5 kgs, if you would normally add 5kgs then increment backwards by 5 kgs.
I personally do not follow what I stated previously but that is what the general set up would look like.
I do not zig zag, at the end of each cycle I work out a new 1 rm on all exercises and then for the 15's I work at 52.5%, 57.5%, 62.5% & 67.5% of that figure, 10's are 70%, 72.5%, 75% & 77.5% , 5's are 80%, 82.5%, 85% with the final session at 88/89% of the new 1 rm, then a few weeks of working at increasing my 5 rm - all these %'s are approximate and generally I work to the nearest 2.5 kgs - this method is probably over complicated (I have to use a spreadsheet) but is what works for me, as how Jester does it is what works for him.
To be honest the easiest way is how Jester proposes.