The first step towards architectural measured drawings was to establish a datum line i.e. a section plane that becomes a horizontal reference plane at which the plan is drawn. Usually this horizontal plane is established at a level of 3 feet or 900mm from the floor level, explaining all recesses, projections and other details, that comprehensively reflect the building and its defects (like settlement, movement of members, inclinations etc). However, in the case of Karen Ghar, datum line was not established with respect to the the floor level, as the latter differed at different parts of the building. Also, a section at 3 feet would only provide partial information of the built profile, hence, the level was selected at an average of 920mm-1000mm from the floor that provided the profile with all openings, niches, recesses, mouldings etc.
Initially the marking was done using a string, white chalk and plumb bob, of which the latter was replaced by a spirit level (manual). The string was held tort at two ends – from a marked point on the building to a corner or point in the building to be marked. The level was checked using a spirit-level for horizontality and marked using the chalk. (Refer to Photograph - Marking the Datum Line along built profile)
|Marking the datum line|