There is one thing that I do with depth, if you look at graphs most small stocks will go up or down about 7 %
So I take the offer price and deduct 10% and do the same with the sale side (add) so in effect I only use the figures which are 10% either side of the buy and sell to be important
This will almost always give a far different figure than the totals at the bottom of the columns because if a stock is selling at $1.00 an offer for 5 million shares at 20 cents is never going to come into contention so should not be used in calculations
Someone posted that they take only the top 3 but I believe that this is far too narrow but if it works for him that's fine we all have to develop our own methods as I also believe that it's all a judgment call or "hunch" anyway