comprising of a circular slide rule marked in blue ISOTOPE CALCULATOR, designed by the isotope division A.E.R.E. Harwell England, along with an original instruction manual titled 'United Kingdom Atomic Energy Authority Research Group, An Isotope Calculator, W. S. Eastwood, 1958; another circular slide rule marked in blue ISOTOPE HANDLING CALCULATOR MKII designed by the isotope division A.E.R.E. Harwell England along with an instruction manual titled United Kingdom Atomic Energy Authority Research Group, An Isotope Handling Calculator, R West, 1958, and another later instruction booklet (5)