A variables double sampling plan

For some time it has been the standard practice in ordering most electronic components to specify a nominal value and a plus and minus tolerance. When these components are used in conjunction with others in electronic equipment, advantage is often taken by design engineers of the fact that the tolerances do not necessarily add up directly. For instance, if we have a circuit using three 1000-ohm plus-or-minus-10 per cent resistors in series, our total value of resistance might turn out to be as high as 3300 dims or as low as 2700 ohms. This of course could only happen when the three resistors were each at the high or each at the low end of the tolerance range.