In 1999 the author reported the results of an 18 year study into the accuracy of sand and gravel reserve calculations. Since that time some changes have been made in the company’s resource investigation practices in certain types of deposit, and the data gathering has continued. The paper presents the results of significantly more data than previously, considered on their own and in combination with those from the first exercise. The analysis shows closely similar outcomes in respect of accuracies, the distribution of results, and the magnitude of excursions from the bulk of results. Conclusions and the statistics from the 1999 study are supported by the greater volume of data, and it can be suggested that attempting to improve accuracy by the last few per cent could be disproportionately expensive.

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