The 30R was the most advanced Rockwell handheld unit to be made at the Portsmouth factory. A 31R also was made, with exactly the same functionality as the 30R, but with (I believe) internal rechargable batteries rather than the 9V battery used on this model. Over and above the 20R the 30R has some arithmetic functions added. Namely square, squareroot and reciprocal. The memory functions are reduced slightly to just + and -, but a new interchange function is extended to swap 'X' with the memory register 'M', as well as an X/Y exchange. Also a useful sign change is added for the first time. Unfortunately, it has lost the indicator that the memory has a value, that the 20R/21R units have, even though the manual suggest that this feature exists (though on the left of the display). The additional functions are accessed by the 'function' button to 'overload' the existing keys.

One other funny discrepency with the manual is that the error conditions (divide by 0, over and underflow) are documented as for the 18R (i.e. all decimal points light up), whereas it actually lights up a square in the ninth digit on the right. I don't know whether the calculators changed functionality in this repsect or whether this is just a mistake in the manual. The manual for the 21R documents this correctly (see manuals page).

This unit came with a proof of purchase certificate (click on the image on the right to see an enlarged version.) This unit was sold on 1st April 1976 (as would be written in the U.K., I assure you), whereas the internal I.C. date is 7452 (1974 week 52), giving over a year an three months from the manufacture of the I.C until the unit was sold. The retailer is given as Kay's mail order LTD, which was (and still is) a leading U.K. home catalogue business, so this unit was not sold in a shop.

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