What instruments are needed to measure the dimensions of small bodies by the row method?

To measure the size of small bodies by the series method, the simplest instruments are needed. For example, a ruler with millimeter divisions. There should be a lot of small bodies when measured in this way. The method assumes that the sizes of the items are equal, or the difference can be neglected. The method itself consists in measuring the size of several objects tightly packed in a row, and then dividing the result by the number of them in the row.