1 - The FTSE 100 is an index of the 100 most highly capitalised UK companies listed on the London Stock Exchange.
2 - The index is maintained by the FTSE Group, an independent company which originated as a joint venture between the Financial Times and the London Stock Exchange (hence the abbreviation FTSE).
3 - The index began on 3rd January 1984 with a base level of 1000.
4 - The highest value reached to date is 6950.6, on 30th December 1999.
5 - The index is calculated in real time and published every 15 seconds.
6 - The FTSE 100 companies represent about 81% of the market capitalisation of the whole London Stock Exchange.
7 - The constituents of the index are reviewed quarterly with the largest companies in the FTSE 250 index being promoted if their market capitalisation would place them in the top 90 companies of the FTSE 100 index.
8 - The FTSE 100 is weighted by market capitalisation so the larger companies have a greater effect on the index than the smaller.
9 - The only working day the FTSE 100 was not functioning was Friday 16th October 1987, the day after the great storm.
10 - The biggest one day fall was on 20th October 1987 when the FTSE 100 fell by 12.22% or 250.7 points, this day is known as Black Monday.