DOUBLE SAMPLING
Definition:
A standard form of sample design for industrial inspection purposes. In accordance with the characteristics of a particular plan, two samples are drawn, n1 and n2, and the first sample inspected. The batch can then be accepted or rejected upon the results of this inspection or the second sample be inspected and the decision made upon the combined result.
Context:
The term has also been used somewhat loosely for what is called multi-phase sampling and the two-stage version of multi-stage sampling. There is a further usage whereby a first sample provides a preliminary estimate of design parameters which govern the size of the second sample to achieve a desired overall result.
MULTI-PHASE SAMPLING
Definition:
It is sometimes convenient and economical to collect certain items of information from the whole of the units of a sample and other items of usually more detailed information from a sub-sample of the units constituting the original sample. This may be termed two-phase sampling, e.g. if the collection of information concerning variate, y, is relatively expensive, and there exists some other variate, x, correlated with it, which is relatively cheap to investigate, it may be profitable to carry out sampling in two phases.
At the first phase, x is investigated, and the information thus obtained is used either (a) to stratify the population at the second phase, when y is investigated, or (b) as supplementary information at the second phase, a ratio or regression estimate being used.
Two-phase sampling is sometimes called "double sampling".
Context:
Further phases may be added if desired. It may be noted, however, that multiphase sampling does not necessarily imply the use of any relationships between variates x and y. The expression is not to be confused with multi-stage sampling.
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Not less than double the highest frequency component of the signal you're sampling.
The idea is to first do the subtraction, then multiply the result by 2.
the number itself
i dont know but a ratio table is easier
The difference between two numbers is determined by subtracting the smaller number from the larger number. For example the difference between 12 and 9 is: 12-9=3. For negative integers, you will see that the difference is the total distance. For example, the difference between (-12) and 9 is 9-(-12) when you simplify by eliminating the double sign, the two minus signs become one plus sign: 9+12=21. More simply put, you will have to travel 12 to get from (-12) to zero, then another 9 to travel the total distance (difference) of 21.