A method of operation of a meter for performing a measurement of an electrical parameter by processing successive samples of an output of a sensor of the electrical parameter, the method comprising, in the meter: sampling an output from the sensor of the electrical parameter to produce at least one sample; and iteratively performing steps of: sampling the output from the sensor to produce one or more further samples; holding in memory a stored array of samples comprising the at least one sample and each of the one or more further samples from each iteration; determining a measure of statistical variability from the stored array of samples for the respective iteration; determining a measure of statistical variability of a mean for the respective iteration from the measure of statistical variability and from the number of samples used to generate the measure of statistical variability; comparing the measure of statistical variability of the mean with a pre-determined threshold; and generating an electrical signal indicating that the measurement has reached or exceeded a target confidence level if the measure of statistical variability of the mean of the samples taken during the measurement is less than or equal to the pre-determined threshold. sampling an output from the sensor of the electrical parameter to produce at least one sample; and iteratively performing steps of: sampling the output from the sensor to produce one or more further samples; holding in memory a stored array of samples comprising the at least one sample and each of the one or more further samples from each iteration; determining a measure of statistical variability from the stored array of samples for the respective iteration; determining a measure of statistical variability of a mean for the respective iteration from the measure of statistical variability and from the number of samples used to generate the measure of statistical variability; comparing the measure of statistical variability of the mean with a pre-determined threshold; and generating an electrical signal indicating that the measurement has reached or exceeded a target confidence level if the measure of statistical variability of the mean of the samples taken during the measurement is less than or equal to the pre-determined threshold. sampling the output from the sensor to produce one or more further samples; holding in memory a stored array of samples comprising the at least one sample and each of the one or more further samples from each iteration; determining a measure of statistical variability from the stored array of samples for the respective iteration; determining a measure of statistical variability of a mean for the respective iteration from the measure of statistical variability and from the number of samples used to generate the measure of statistical variability; comparing the measure of statistical variability of the mean with a pre-determined threshold; and generating an electrical signal indicating that the measurement has reached or exceeded a target confidence level if the measure of statistical variability of the mean of the samples taken during the measurement is less than or equal to the pre-determined threshold.