Typewriters, musical boxes, calculators and other items of technical apparatus and mechanical music can be valuable and much sought after by collectors.
According to Mr Christopher Proudfoot, a specialist in technical apparatus and mechanical music and a director of Christie's, old typewriters can be worth up to £5,000 sterling (€7,655).
If the design of your typewriter is different from the conventional design, it could be valuable.
But "if it's a normal conventional design like an Underwood or a Remington or a Corona or whatever, it's not going to be worth very much. It has to be significantly different."
The best thing is to "think of what constitutes the conventional type, such as the Underwood. They have four rows of keys which operate typebars which hinge up and strike the front of the platen - the curved roller that the paper goes around."
That is the conventional typewriter. Anything that is different from that could be of interest to collectors.
For example, "most Hammonds are not terribly rare and desirable", but one of the very first type, patented in 1880, was estimated at £800 to £1,000 in a recent auction.
It has a curved keyboard and there are only two rows of keys which are "shaped rather like piano keys and made of ebony. And instead of typebars that come up, the typeface is cast into a sort of part-circular sector, looking a bit like a brake shoe. So it's completely different."
However, most Hammonds are from the early 20th century and these tend to be worth £100 to £150 each, he says.
Mechanical music comprises musical instruments "which play themselves in one way or another, mostly from some form of revolving disc or cylinder. In fact, it's a precursor to the computer", which is "basically a musical programme which performs every time you play it", he says. Examples include musical boxes, jewellery boxes, barrel organs, gramophones and phonographs.
A coin-operated zon-o-phone, a very early gramophone, dating from around 1902 was recently estimated at £2,500 to £3,000. "It was an early rival to the gramophone. The gramophone itself was originally a trade name but it's become generally in use later on. Because it's operated by a coin, it would have been on a bar top in a pub or somewhere like that originally. It makes it much more interesting to collectors than just an ordinary one".
Mechanical calculators mostly dating from the late 19th and early 20th century come in various forms.
"You can't generalise. Some of them are really just slide rules. There's one we get quite often, a circular thing, which is effectively a circular slide rule. Instead of having a long slide which you have to pull out, you've got a cylinder with a sleeve on the outer side and the scales are marked on the sleeve. And you just turn the thing around and slide it up and down a bit."
One of the best known calculators, the Fuller's, was recently estimated at £150. "The most expensive one we've ever had", a 19th century mechanical computer, "fetched something like £150,000. But that's very much the top end.
"The vast majority of commercially-manufactured calculators are between £20 and £2,000," says Mr Proudfoot.
Readers can contact Mr Christopher Proudfoot by telephoning 0044 171 321 3272.
