If it is fuel burn then this is roughly how I see the figures.
But you ask about contingency. That is pretty much laid down by your airline and the regulatory authorities. If it is fuel in the tanks you mean, you won't arrive with much less than ten tonnes but my recall is less than perfect.
Funny about the old QOTS, you rarely see a question about her these days. Almost as if she did not exist. And as for KSEA (and even CYVR), two of my favourite haunts. Fine old runs, both of 'em and what fun the -200 was. A doddle.
But that's thread drift if ever there was an example. Pat the pig for me and spend an hour or two in and around Pioneer Square. Watch the lusty floatplanes up at Kenmore Air on the Lake, nobody is looking so enjoy a beer in Hooter's and tut tut about it afterwards. Tell me if the model railway is still in the bar opposite the Green Tortoise. And if you go to CYVR up the road, it's the steam clock, Gastown and the blue trail up Grouse Grind for you. And a swing on the suspension bridge half way back to the ferry. Tee Hee.
What a privilege and what memories to have been a QOTS driver.
My graph is for factory fresh by the way.