Slipsticks

My Pickett N901-T, set to show 1.5 x 4 = 6

As long as man has had money, man has been counting. From counting, simple arithmetic followed, and soon after that mathematics (the study of structure in numbers) was born. As far back as Babylon and Egypt we know they used algebra and geometry to do taxes, finances, engineering, astronomy, and other tasks. How did they do it without calculators?