Most sources estimate that the deep Web is several orders of magnitude larger than the surface Web. An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the (base 10) exponent being applied to this amount. Thus a repair bill of a thousand dollars (10^3) is 2 orders of magnitude greater than a bill of 10 dollars (10^1). In ordinary English usage "several" means roughly "an indefinite number more than 2 or 3 but not many". So 500:1 is not an unrealistic ratio.