who were also responsible for construction in Stage III. Hornibrook manufactured the 2400 precast ribs and 4000 roof panels in an on-site factory and also developed the construction processes. The achievement of this solution avoided the need for expensive formwork construction by allowing the use of precast units and it also allowed the roof tiles to be prefabricated in sheets on the ground, instead of being stuck on individually at height. The tiles themselves were manufactured by the Swedish company Höganäs Keramik. It took three years of development to produce the effect Utzon wanted in what became known as the Sydney Tile, 120mm square. It is made from clay with a small percentage of crushed stone. Ove Arup and Partners' site engineer supervised the construction of the shells, which used an innovative adjustable steel-trussed "erection arch" (developed by Hornibrook's engineer Joe Bertony) to support the different roofs before completion. On 6 April 1962, it was estimated that the Opera House would be completed between August 1964 and March 1965. Stage III: Interiors Stage III, the interiors, started with Utzon moving his entire office to Sydney in February 1963. However, there was a change of government in 1965, and the new Robert Askin government declared the project under the jurisdiction of the Ministry of Public Works. Due to the Ministry's criticism of the project's costs and time, along with their impression of Utzon's designs being impractical, this ultimately led to his resignation in 1966 (see below). The cost of the project so far, even in October 1966, was still only A$22.9 million, less than a quarter of the final $102 million cost. However, the projected costs for the design were at this stage much more significant. The second stage of construction was progressing toward completion when Utzon resigned. His position was principally taken over by Peter Hall, who became largely responsible for the interior design. Other persons appointed that same year to replace Utzon were E. H. Farmer as government architect, D. S. Littlemore and Lionel Todd. Following Utzon's resignation, the acoustic advisor, Lothar Cremer, confirmed to the Sydney Opera House Executive Committee (SOHEC) that Utzon's original acoustic design allowed for only 2,000 seats in the main hall and further stated that increasing the number of seats to 3,000 as specified in the brief would be disastrous for the acoustics. According to Peter Jones, the stage designer, Martin Carr, criticised the