He is estimating just like us... nothing official or concrete.
If we use the actual NPD sales with the ratio XB1 showed when MS give us some numbers... I will estimate:
US: 24.5m
63% = 38.9m WW
He is probably using a 60% ratio that give 40.8m.
I think he has access to more numbers than us from more countries. So he's not simply using the 60% thing, he would have specified if he did.
Zhuge's estimates are the most accurate Xb1 estimates we'll ever get. XB1 was probably under 35M at the end of 2017 and over 41M now (he said they were just rounded to nearest million). It probably sold something like 6.5M last year, so a much bigger decline outside of the US compared to 2017.
It's the same number chertZ use. Interesting
Chertz had xb1 about 2 million higher but just adjusted it down to match this.
Spain 2018 Hardware:
PlayStation 4: <650.000
Nintendo Switch: <390.000
Nintendo 3DS: <75.000
Xbox One: <73.000
It says less than but its pretty much those figures, I believe.
Just to add to this, We know Switch LT sales are 730k, so Switch 2018 was up around 15% from 2017 in Spain. So yeah, its looking like 15-20% is the WW number.