Sinclair Scientific

The Sinclair Scientific calculator was a 12 function, pocket sized calculator, selling for about $100. It was introduced in late 1974 and sold in both kit and assembled forms.

Power was supplied by four AAA sized alkaline cells. A common failure mode of these calculators was breakage of the battery contacts, but Sinclair was quick to respond by referbishing any calculator with this problem for free (although you did have to pay the shipping to them).