In order to analyse the records thoroughly I have devised a spreadsheet for use on a PC, specially adapted to the requirements of this sort of repeated survey. The analysis methods are different from the standard ones, partly to suit the nature of the data, and partly to make the computations simpler. Records from visits were transferred from a standard Butterfly Site Recording Form into the same format on a customised Microsoft Excel spreadsheet, an excerpt of which is shown above, with one worksheet per year. Rather than using a week as the basic unit I have chosen one-third of a month (which I call a "thirding") consisting of 10 days, except at the end of 31-day months when they consist of 11 days. It is much easier to compute which thirding the date of a visit falls into, given day and month, than the week. The recording year stretches from 1 March to 31 October (rather than the conventional April to September, which would waste a lot of data), giving 24 thirdings in the recording year. There may sometimes be more than one visit within a thirding, so the number of sightings is taken as the largest in any one visit within a particular thirding. An algorithm converts the data on the recording form into this standardised reduced format.

Another worksheet then picks off the data for all the years and displays it as a table, species by species. The numbers are colour-coded for ease of interpretation (see Site and Surveys). The colour coding does not follow the convention used on recording forms of A = 1, B = 2 - 9, C = 10 - 29, etc., because nearly all the data would be either A or B. Instead, Yellow = 1, Orange = 2 - 5 ("several"), and Red is 6 or more ("many"). A distinction is made in the species tables between thirdings in which no visit was made (left blank), and those when a visit was made but none of that species were seen (indicated 0). To the right of each table are totals of numbers seen per year, which were subsequently carried across to create the 5-year summary table. Below the table are the mean numbers seen in each thirding, averaged over just those years with a "filled" thirding (including zeroes). An adaptation of the colour coding is used for the mean and total numbers.

The species are grouped three to a page under suitable headings, sometimes with a species appearing in more than one grouping. The mean values are plotted graphically for the three species below the tables, to show the varying abundance through a typical year. A cut-down example is shown below.