Color ultrasound is subject to a few millimeters of error. Color ultrasound is an important obstetrical test, and the main components of an obstetrical ultrasound include the biparietal diameter, abdominal circumference, head circumference, femur length, and amniotic fluid depth. All of these values are measured by manually finding the right cut surface to freeze and then finding the two points that need to be measured for the measurement. During the measurement process, there may be an error of a few millimeters, related to the standardization of the cut surface, the precision of the examination instrument, and the consistency of the probe pressurization. Color ultrasound is the simplest, non-invasive test in obstetrics. All measurements are subject to a certain degree of error, but as long as it is within a reasonable range, there is no need to worry too much.