Inevitably **things change** over time.
In some respects the text of the original book shows its **age** and some **details** now look slightly out of place.
In producing this web site I have generally opted to retain the **original text**.
These notes are intended as **pointers** to a few areas where some additional comment may be appropriate.

First, **units**. Here and there, examples refer, for instance, to **feet** or to temperatures in **Fahrenheit**.
Nowadays, most children are likely to be taught about **metres** and degrees **Celsius** and may not encounter feet or degrees Fahrenheit at school.

Second, the **octal** number system.
Those going on to delve further into computing are now relatively unlikely to see octal in practical use but are very likely to encounter the **hexadecimal** system, **base 16**, with symbols **0 to 9, A, B, C, D, E and F**.
The principles are identical, hexadecimal just uses a different base and more symbols and **one hexadecimal digit** corresponds to **4 binary digits**, not 3 - so two hexadecimal digits constitute one, 8 binary bit, **byte** - nowadays the most commonly encountered unit of computer data.

Hexadecimal / base 16 is, in fact, briefly introduced on the very last page, Page 460 though under the, now archaic, name of *sexadecimal* and using symbols *+*, *-*, *j*, *n*, *l* and *t* to represent *10*, *11*, *12*, *13*, *14* and *15* rather than the, now conventional and probably less confusing, *A*, *B*, *C*, *D*, *E* and *F*.

Third, **logarithms** and the **slide rule**.
Log tables and slide rules are now history - **pocket calculators** and **computers** have taken over.
But for anyone engaged in **mathematics**, **physics**, **engineering** and many other subjects, the understanding of the concepts of **powers**, **exponents** and **logarithms** is still as **relevant** as ever.

Fourth, **gender**.
Some of the text uses **he / his** rather than **she / her**.
When the book was, originally written, that was probably the norm.
Readers should mentally **substitute** whatever **pronouns** they feel appropriate as they read.
They should certainly bear in mind that **girls** are quite as **capable** in this field as **boys** - indeed, the **first computer programme** was arguably written by a lady, **Ada Lovelace**.

Fifth, original **spellings** have been retained - e.g. "realize", rather than "realise".

I have, however, corrected a few **typographical errors** in the original text.
Any errors that remain are either ones I failed to spot in the original or ones which I have inadvertently introduced.
Please let me know about any you notice and I will endeavour to correct them (email : **info@arithmeticofcomputers.co.uk**).

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David Nutting
Tenscope Limited
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