Why I shouldn't go on YouTube

I found a pattern for a sweater, and it's the sort of sweater I love.  It's baggy and roomy and saggy and entirely my style (such as it is).  It has room for the lumps and bumps and I suppose you could dress it up and down if you wanted.

I found it on YouTube here but there is also a free pattern on Red Heart here also I wish Red Heart was easier to find in the UK because it looks like they have awesome yarns

It's knitted in the equivalent of Aran.  I have some lighter weight double knitting space dyed yarn that I have been wanting to use but space dyed always looks a little odd when you divide for the neck.  This pattern doesn't divide for the neck.  You can see where this is going.  I'm getting a bad case of 'I can just...'  as it, I can just knit a swatch with double knitting yarn on 4mm needles, work out roughly how many stitches I get to 10cm, look at the size guide on the pattern and bless them they have the measurements of each piece shown, do some sums, get bear to check them and it should be easy - right?  There isn't even any shaping, so how hard can it be - right?  I can just knit a sweater pattern drawn up for aran weight yarn in double knit weight yarn, probably, possibly, if bear checks the sums...

Today bear's maths tutor was explaining things like calculating area and volume.  They both seemed to have a blast, especially converting from Imperial to metric and back.  I just left them with juice for bear, coffee for the awesome tutor and biscuits.