Rockwell 21R.

9v (PP3).

Display is 8 digits, red LED.

Four function, %, memory.

Chip is Rockwell A5300PD, here date coded mid-1975.

76 x 153 x 23 mm (3.0" x 6.0" x 0.9").

Made in Great Britain, at the former Sumlock-Anita factory in Portsmouth.  See the page 'The Rockwell Connection'.

Inside, showing the circuit board. The LED module with the moulded-in lenses is towards the top, while the Rockwell integrated circuit is towards the bottom.