The Wood Computer

by Jo Brodie, Queen Mary University of London

A wooden woodland bridge with trees in the background.
Image by Peter H from Pixabay

Punch cards inspired Babbage as he invented the first Victorian computer, and were a way the first computers stored data a hundred years later. Variations, called edge-notched cards, had their uses before the first working computers, though. They provided an efficient way to look up information. One use was to help identify timber: Oxford’s human-operated ‘wood computer’ was used in forests world-wide.

Interested in nature and enjoying a nice walk, you come across an unfamiliar tree, and want to identify it. How do you do it? You might work through a set of questions, first looking at the leaves: what shape are they, what colour, do they have stalks, do they sit opposite each other on a twig or are they diagonally placed, and so on. You then move to questions about the bark… Gradually, you narrow it down to one tree. What, though, if your job is to check that your company is buying the right timber and the tree is cut up into logs (no leaves or bark)? The task is the same, going through a checklist of questions, just harder unless you are an experienced botanist. Now you consider things like the pattern of the grain, the hardness, the colour and any scent from the tree’s oils.

Historically, one way of working out which piece of timber was in front of you was to use a wood identification kit or ‘wood computer’. This was prepared (programmed!) from a pack of index cards with 60 or more features of timber printed on them. However, they weren’t just cards to read but cards to compute with.

Holes and notches

The cards were special because they had regularly placed holes round all four sides. Each card had notches cut into different holes. Each feature of the timber was linked to one or more holes. The features were grouped together around related properties: so, for example, all the possible colours of timber might be grouped together on one section of the card. Properties about how fine-grained the timber is would be grouped in another section.

Each card represented one type of wood and the ‘programmer’ of the cards would notch the holes next to the features that defined it. If a particular type of timber was fine-grained you would add the notch to the hole next to “fine-grained”, if it wasn’t that hole would be left un-notched. Notches were added for all relevant timber properties making each card unique, with a slightly different pattern of notches, uniquely describing the features of the tree it represents. (See an example of an edge-notched card below.)

How it works

To use a wood computer, take the pile of cards, pick a feature of the timber in front of you and insert a thin knitting needle into the hole linked to the feature. Then lifting the pile up shake out any cards with notches in that hole. All of the cards for timber that don’t have that feature will have an un-notched hole and will hang from your knitting needle. All cards representing timber that does have that feature are now sitting on the table. Yours is somewhere amongst them. If your timber is NOT fine-grained then instead, when you put the knitting needle in the fine-grained hole, keep those left on the knitting needle.

You repeat the process several times to whittle (sorry!) your cards down, each time choosing another feature of the timber in front of you. Eventually you have only one card left and have identified your timber.

Just the cards for the job

The cards are incredibly low tech, requiring no electricity or phone signal and are very easy to use even without specialist botanical knowledge. All the knowledge is programmed into them. You also find the answer very quickly. Margaret Chattaway, a botanist at the Imperial Forestry Institute, Oxford, in the 1930s realised that was exactly what was needed for their team inspecting timber and so the original wood computer was created.

So next time you are out for a walk, make sure you have your knitting needle and a suitable pile of cards with you. Then identifying trees, birds, fungi or even animal poo will be so much quicker and simpler.

An edge-notched card for Bob Marley and the Wailers notched as a Reggae Group with initials B-M-W: those three letters are notched, the other letters are un-notched.

Why not create an edge notched card system for something you are interested in, for identifying birds perhaps or quickly finding details of films, or music or of something you collect?

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This article was funded by UKRI, through Professor Ursula Martin’s grant EP/K040251/2 and grant EP/W033615/1.

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