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This 18th/19th century ivory slide rule sold for £9500 at Tamlyns in Bridgwater.

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Nearly 400 years after William Oughtred (1574-1660) invented the ingenious little mathematical computers they are now redundant – but not without value.

The late 18th-early 19th century ivory example illustrated here was offered at Tamlyns (18% buyer’s premium) at Bridgwater on May 10.

It had the unusual feature of two slides, for extra complicated calculations, and although it bore no maker’s mark, came in its original pressed card case and was in excellent condition.

Pre-sale interest in the rule estimated at £300-400, translated into bids in the room and on the phone but it became evident that two collectors bidding online were determined to have it.

One did with a winning bid of £9500.