Abstract: In making semiconductor devices such as integrated circuits, semiconductor wafers are often sorted according to both their thickness and their resistivity. To so sort the wafers they are moved successively along a first track to a thickness determining device which produces a signal indicative of the thickness of each wafer. This signal is stored by a computer. Continued successive movement of the wafers brings them to a resistivity determining device. This device, which is rendered effective by the stored thickness signal, produces a signal indicative of the resistivity of each wafer. The resistivity signal is stored by the computer. The successive movement of the wafers is continued along the first track to move them onto a second track. Each article is moved successively along the second track. And, in response to the stored signals, each article is moved into a preselected position associated with both the thickness and the resistivity of each article.