This is a circular brass calculator which was Patented by H and M Dickinson in early 20th century . (Bri Cal -British Calaculator). Using the stylus, one rotates the chain, until the wanted sums show in the window. Sums can be calculated to £499.19s.11 1/2d. The calculator comes in it original red velvet and felt lined box. The box is marked on the outside and inside Brical Money Calculating Machine. The machine is marked The British Calculators Ltd, For Compound Addition, Patent. The British Calculator company was of Belfast Road Stoke Newington, London.