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Historical records reveal that approximately 1 __________ ago great civilisations in the Middle East and North Africa began to make clocks to 2 _____________ their calendars. These cultures found that they needed to organise their time more efficiently. Originally 3__________and sticks of incense that 4 ___________ at approximately predictable speeds were used to estimate 5______________________ . Other methods were 6______________ . The development of 7________________ in the twentieth century led to clocks with 8_____________ at all. Now mechanical clocks have since come to be largely powered by 9________________ , removing the need for 10____________.