Sumlock Anita Electronics Ltd. started making Rockwell calculators after they were bought by Rockwell International in 1973. The 10R is the least sophisticated of the Rockwell calculators made at the Portsmouth factory. The image on the right (click to enlarge) is of a contemporary advertising poster showing a range of the rockwells, from the 10R (left most in group) to the 61R, the main image being of a 20R This particular 10R calculator has an I.C. date stamp of 7514 (week 14, 1975). It is smaller than the others, with only four rows of keys, and no dedicated equals key---the plus key doubles up for this function. So adding two and three becomes 2 += 3 +=. This is effectively using the natural chaining that exists in the calculators, where the equals key is in fact redundant. Not mentioned in the manual, but if one wishes to continue a calculation after the += has been pressed, then by pressing 0 before the desired function will allow further processing. So, for example, if after the sequence 2 += 3 +=, one wishes to multiply the result (which is 5) by 6, then press 0 x 6 +=, to give 30. Try it out on the above image---it works!