Science and engineering

A thick ring-like shell object found with four slits each in two margins served as a compass to measure angles on plane surfaces or in the horizon in multiples of 40 degrees, up to 360 degrees. Such shell instruments were probably invented to measure 8–12 whole sections of the horizon and sky, explaining the slits on the lower and upper margins. Archaeologists consider this as evidence that the Lothal experts had achieved something 2,000 years before the Greeks: an 8–12 fold division of horizon and sky, as well as an instrument for measuring angles and perhaps the position of stars, and for navigation.[15] Lothal contributes one of three measurement scales that are integrated and linear (others found in Harappa and Mohenjodaro). An ivory scale from Lothal has the smallest-known decimal divisions in Indus civilization. The scale is 6 millimetres (0.2 inches) thick, 15 mm (0.6 inches) broad and the available length is 128 mm (5.0 inches), but only 27 graduations are visible over 46 mm (1.8 inches), the distance between graduation lines being 1.70 mm (0.067 inches) (the small size indicates use for fine purposes). The sum total of ten graduations from Lothal is approximate to the angula in the Arthashastra.[16] The Lothal craftsmen took care to ensure durability and accuracy of stone weights by blunting edges before polishing.[17]
For their renowned draining system, Lothal engineers provided corbelled roofs, and an apron of kiln-fired bricks over the brick face of the platform where the sewerage entered the cesspool. Wooden screens inserted in grooves in the side drain walls held back solid waste. The well is built of radial bricks, 2.4 metres (7.9 ft) in diameter and 6.7 metres (22 ft) deep. It had an immaculate network of underground drains, silting chambers and cesspools, and inspection chambers for solid waste. The extent of drains provided archaeologists with many clues regarding the layout of streets, organization of housing and baths. On average, the main sewer is 20–46 cm (7.8–18.1 inches) in depth, with outer dimensions of 86 × 68 × 33 cm (34 × 27 × 13 in). Lothal brick-makers used a logical approach in manufacture of bricks, designed with care in regards to thickness of structures. They were used as headers and stretchers in same and alternate layers. Archaeologists estimate that in most cases, the bricks were in ratio 1:0.5:0.25 on three sides, in dimensions which were integral multiples of large graduations of Lothal scale of 25 mm (1.0 in).