Gyroscopic Investing

seems GTU deviates from the its NAV quite a lot and quite often (large premium changes)
I checked today's valuation,
based on the new york spot price at 5:00pm ($1506/oz), the GTU is trading with a discount of 0.65%
https://spreadsheets.google.com/spreads ... true&gid=0

however, on the fund's website, the nav is calculated with london fix price $1489.50/oz, therefore the GTU is trading at a premium of 0.5%.

how likely is there a big price difference between the london and NY? I wonder if that's part of the reason of the high variability.

Recently I move from CEF to GTU, but I'am a bit confused for how this this fund is moved:
Yesterday gold price is up but GTU down. Today gold down but GTU up.
What I missing here?

I have too a litle of IAU for rebalance purposes and this ETF moves correlated to the gold price yesterday and today. 

The premium fluctuates, but I would rather buy it when the premium is near zero (as it is now) than when it was closer to 10%.