Sentence:  This negative pressure is not explained by the velocity head * * f since this is not sufficient to explain the readings by several <WSD>magnitudes</WSD> . 
Meaning of the word marked with <WSD> tags:  a number assigned to the ratio of two quantities; two quantities are of the same order of magnitude if one is less than 10 times as large as the other; the number of magnitudes that the quantities differ is specified to within a power of 10