MR Jenkins, Gwbert, claims many people think it is a new decade and choose to ignore simple, logical arithmetic, which runs from one to 10 and asks how a decade can start with 2020 ('2020 is NOT a new decade', Western Telegraph letters January 29).

But surely by asking such a question suggests a misunderstanding of the word decade, a confusion of our decimal system of numbering and an apparent lack of understanding of cardinals and ordinals.

Firstly, in dealing with the meaning of the word decade the answer is quite straightforward.

A decade is simply a period of 10 years, and therefore can start with any year such as 2020, 2013, 1949 or 1066 etc.

The following are some uses of the word decade: air traffic has increased 30 per cent in the last decade. Her acting career spanned almost six decades. India attained independence in 1947, after decades of struggle.

We are also familiar with terms such as the ‘Swinging 60s’ meaning a 10-year period from 1960 to 1969.

Therefore, a decade can start with any number ranging from 0 to nine, and simply defines any 10-year period.

Secondly, in an effort to further clarify the issue, the number system (decimal) we use every day is based on 10 digits using the numerals, 0,1,2,3,4,5,6,7,8,9. It is very important to note it does not use the numerals, 1 to 10, thus the decimal system starts with the numeral 0 and we should logically count from this numeral. But in our everyday arithmetic we regard the numeral 0 as zero, or nothing.

Thus, if we had a bag of 10 oranges, we would count from one to 10 and not 0 to 9 and you cannot go to the shop and buy zero oranges, so yes, I guess it is confusing.

The reason we don’t count from zero in our everyday life is because early cultures such as the Greeks, for example, did not have a concept of zero, although the Mayans did - the Mayan system of counting was based on the number 20, using the numerals 0 to 19 and as such their year was divided into 18 months of 20 days each, totalling 360 days - a special period of five days at the end, called Uayeb, brought the count to 365. The Mayans started the first day of the month with Zip and the next day (second) was 1 Zip, the following day was 2 Zip, and so forth, until they reached 19 Zip.

Except for the Mayans nobody else had a year zero or started a month with day zero - and it is said the Mayan calendar was superior to our calendar.

To understand number systems an excellent book to read is titled, ZERO, the biography of a dangerous idea by Charles Seife.