Ordinate, or datum, dimensions measure the perpendicular distance from an origin point called the datum to a dimensioned 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. If you specify a point, AutoCAD LT automatically determines whether it is an X- or Y-datum ordinate dimension. This is called an automatic ordinate dimension. If the difference between the feature location and the leader endpoint is greater for the Y value, the dimension measures the X value. Otherwise, it measures the Y value. AutoCAD LT uses the absolute coordinate value of the current UCS to determine the ordinate values.
The dimension text is aligned with the ordinate leader line, regardless of the text orientation defined by the current dimension style. You can accept the default text or supply your own.