Systematic resistance as errors as shown, with the use of normal instrumentation seems impossible to get that simultaneously the two instruments are requested by the authentic electric magnitudes tension and intensity. It is inevitable, therefore, that each one of the two connecting this measuring erroneously. If this contingency is ignored, it is clear that, regardless of the inherent accuracy to the indication of the instruments, is would be introducing an element of distortion, which we call systematic error, which increases the uncertainty of the measurement process with its amount. However noteworthy that, in either of the two connections, the sign of the systematic error is known and even its value may be quantifiable, being thus possible correction of the result and the almost total elimination of that error. Let’s see: In the short connection: the current flowing through the element unknown Ix is the difference between which circulates through the ammeter, and therefore indicated by this, and it consumes the voltmeter, i.e.: Ix = I – Iv while the applied to the element to measure potential difference coincides with the voltmeter. UX = U and dividing Member to Member both equalities gives: Gx = accumulators 7.1 Gv being Gx and Gv conductances incognita and the voltmetric instrument respectively. Therefore the value obtained by dividing the readings of both instruments will correspond to the parallel equivalent of the element unknown and voltmeter, which means a sum apparent conductance of both and a systematic error by conductance excess and defect in resistance.
And the relative: 7.5 in either of the two types of connection, the accuracy of the measurement result depends on equitably precision that ensures each of the two instruments as well as the accuracy with which the value of the internal resistance of the systematic error that causes measuring instrument is known. Applying the techniques of calculation of errors to exact expressions 7.1 and 7.4 is obtained for the connection short: 7.6 and using assumptions less conservative and more realistic, the previous expression is: 7.6 Bis and to the long connection: 7.7 7.7 bis as you can see, the previous expressions appear a few ratios of resistances that increase the value of the uncertainties, and that match the expression and the value of systematic errors, and therefore and to the extent that they may be large or smallthe accuracy will be affected although the systematic error is corrected. Therefore, a first selection criterion of connection can be set by opting for one of the two that a priori present one less systematic error.