A bifilar eyepiece in which the motions of both cross-wires are digitised is described. This enables the readings to be punched out automatically on to computer tape. A novel form of crosswire is also employed. It is found that the co-ordinates of a grain in the emulsion can be measured with an accuracy of 0.05 μ for each axis. It is also shown that the error introduced by digitising is much less than the setting error of the cross-wires on a grain image.