 Sinclair would shortly stop producing calculators and instead focus on computers , starting with the <unk> in 1977 . The loss of the calculator market was due in part to technological development leading to smaller and cheaper components , which put heavy pressure on profit margins . An import levy of up to 17 @.@ 5 % was placed on components , but the duty for calculators imported from Japan or Hong Kong could be as little as 5 % , making it unprofitable to produce calculators in the UK . Sinclair also had some problems with the reliability of earlier calculators that had adversely affected its reputation , but the Sovereign was sold with a " full and unconditional " five year guarantee . 
