 The Sovereign was one of the last calculators produced during Sinclair 's foray into the calculator market that had started with the Sinclair Executive in September 1972 . The Executive had <unk> for GB £ 80 when introduced , but in little over a year it was possible to purchase a Sinclair calculator for GB £ 20 and by November of 1976 a model was available for GB £ 4 @.@ 95 . Cheaper calculators with liquid @-@ crystal displays instead of light @-@ emitting diodes were becoming more popular , and had much longer battery lives of months or years . Such calculators were available for well under GB £ 10 , with all the functionality of the more expensive models . The impossibility of selling " simple " calculators <unk> led Sinclair to introduce models such as the Cambridge Scientific , introduced in August 1975 at a price of GB £ 29 @.@ 95 . 
