Ordinate dimensions measure the perpendicular distance from an origin point called the datum to a feature, such as a hole in a part. These dimensions prevent escalating errors by maintaining accurate offsets of the features from the datum.
Ordinate dimensions consist of an X or Y value with a leader line. X-datum ordinate dimensions measure the distance of a feature from the datum along the X axis. Y-datum ordinate dimensions measure the distance along the Y axis.
After you specify the feature location, you are prompted for the leader endpoint. By default, the leader endpoint that you specify automatically determines whether an X- or a Y-datum ordinate dimension is created. For example, you can create an X-datum ordinate dimension by specifying a location for the leader endpoint that is closer to vertical than horizontal.