Mason-Dixon Line (as known as Mason and Dixon line) is separation boundary between Pennsylvania and Maryland in the United States. It was first introduced just before the civil war period with the introduction of Ohio River, where the Mason-Dixon Line is regarded as the line that separates the slave states in the south and the free-soil states in the north. In 1820 the name of the line was introduced in the debate of Congress that lead to Missouri Compromise. It was named after two Englishmen namely Jeremiah Dixon and Charles Mason who surveyed nearly 375 km line parallel to co-ordinates 39°43’ N for defining the boundaries of two overlapping lands which are Calvert and Penns. In the past, there were many disputes that arose about the claims of the territory from the westward of Delaware River. In the year 1632 Cecilius Calvert was granted by King Charles I for the establishment of a colony towards the north side of Virginia which is under 40 degrees of north latitude and towards the west of Potomac. In the year 1681, William Penn obtained the area surrounding 43 degrees north and the line that goes west from a circle drawn at a distance of twelve miles from the New Castle to 40 degrees north. In the next year, William Penn also received access to the peninsula that was previously claimed by Lord Baltimore. In the later days of 1685, the king ordered to divide the territory equally and thus the western half was given to Baltimore. Then some controversy with the lands happened between the lords and finally in the year 1750 Chancellor Hardwicke given the order that the boundary in the south of Pennsylvania must be a line that runs towards the west from a particular point which is the intersection of the line that divides the Delaware peninsula and tangent to the circular arc of radius of 19 km taken from the centre of Newcastle. Dixon and Mason again looked at the tangent line of Delaware and the arc of Newcastle arc in the year 1765 and then the tangent is extended to the east-west line to tangent point at a location of approximately 39°43′ North. Through the Mason and Dixon planted milestones which are brought from England and every 5th stone has the picture of arms of Penn on the east side and the arm of Baltimore on the west side. The total line was completed by the year 1768, and it took a total cost of $75,000. Again, in the year 1779 both states, Pennsylvania and Virginia, have agreed to extend the line further in the west of five degrees to the Delaware River. The Mason-Dixon Line is still considered to be a demarcation line for the four states which are Delaware, Maryland, Pennsylvania and West Virginia. In the later days it is known as the separation boundary of Northern US and Southern US. Mason and Dixon have performed the work of defining the boundary as accurate as Nevil Maskelyne by using the same instruments. The researchers of British Scientific establishment in the Royal Society of Britain were very much interested in the works of surveyors, especially Henry Cavendish, who maintained regular communication with the surveyors during the work. This types of survey works are performed by point to point line, and then it has been surveyed back to the starting point. In normal cases the return errors are random, but Mason and Dixon found that there was significant amount of systematic errors and when this information got into the royal society then they considered that the error must be due to gravitational pull Allegheny Mountains. Then Mason measured the gravitational force and surveyed on Schiehallion to determine the density of the Scottish mountains, and thus systematic error has been removed.