Thanks Sunny, I've used asof before but to get a cumulative value where using the cumulative tick box doesn't work with distinct values on a chart.
I'm not quite clear how I could use it here though.
I'd like my line chart/straight table to show for the week year as a dimension so for 012016 the % YOY difference to only 012015 not the full year between those dates. The 2nd marker 022016 sowing YOY difference to 022015 etc.
I can't figure out how to write the expression even using variables so end up with two years worth of data on my chart.
thank you for your reply, apologies if i'm missing the obvious!