We receive constant requests, mostly from radio stations, to provide listings for particular months in history. Monthly charts have never been compiled; this prompted us to back-calculate the 'new' monthly charts. These were then split into three sub-divisions; early, mid and late to allow more specific hit listings on the (rare) occasions upon which these are needed.

Computation of the charts is a complex process which recognises a track's performance right across the time period in question. We are indebted to a number of individuals and organisations who were able to let us have benchmark data for sales. Whilst the charts are inextricably linked with retail success, additional 'hit quality' is recognised by popularity in polls, requests and rate of radio rotation. Again, we are grateful to those people who have kept historical data and who made this available to us.

Chart purists who closely scrutinise the movement of every title week by week will probably not approve of our methodology. Our Retrocharts are simply meant to present an entertaining and user-friendly record of the singles enjoyed by the great British public at any period in the past 50 years. Of course, the highest position attained in the Retrocharts does not necessarily tally with the peak position in our main database which is based on weekly performance.

We are keen to know who uses the charts - and for what; please inform us if you use them on a regular or frequent basis. Feel free to suggest improvements.