AKA: ANITA MK 12, OPERATING INSTRUCTIONS, Sumlock Comptometer Ltd, AKA (Label): 21/2M/5/68 BP., Product number (P/N): 212M568BP (21/2M/5/68 BP.),
Keywords/Tags: 212M568BP (21/2M/5/68 BP.)
Date of intro: may-1968, Origin: United Kingdom (List), Dimensions: 280x200mm,
Classification: / Documentation / Instructions,
Related with: SUMLOCK ANITA ELECTRONICS: Anita MK12 (version-2),
#Pags: 22,
Info: The document explains the controls, basic arithmetic and advanced techniques through worked examples showing entries, register selections and displayed results.
The calculator uses three registers.
Register I serves as the display and keyboard-entry register, while registers II and III are interchangeable internal registers for calculation, storage and accumulation.
Grey controls operate on the selected register; green controls work with the other register. This allows one register to hold a constant or running total while the other supports calculations.

The display contains twelve number tubes and ten decimal-point positions.
The manual specifically notes that the rightmost tube belongs to the internal calculating system, normally displays zero and does not form part of the result.
Part I: Basic Operation covers:
- Addition and subtraction in either internal register, including reading negative results through the complement-read control,
- Multiplication, chained calculations and repeated use of a constant multiplier,
- Accumulation of products, rounding to two decimal places and commercial calculations such as applying discounts,
- Division with either the dividend or divisor entered first, including constant divisors and constant dividends,
- Checking and recalling operands, exchanging register contents and correcting entries without losing stored values.
Part II: The Ring Decimal Point and Maximum Capacity Operation explains the machine’s distinctive method of handling very small and very large numbers.
The decimal-point indication can wrap around the display, allowing significant digits to remain visible.
The operator must interpret the indicated position to determine the number’s correct magnitude. Further examples show how to reposition intermediate results to preserve accuracy during long multiplication sequences.
The manual also describes safeguards that lock the controls when certain invalid operations are attempted, together with procedures for releasing the lock and continuing the calculation.
It ends with a directory of Sumlock offices providing sales, service and training throughout Britain and Ireland.