The Total column shows the total number of people in that county or town with this surname. For example, there were 67 people called BUIE in Argyllshire at the time of the 1881 census.
The Frequency column shows the percentage of people in this county or town with this surname. For example, a frequency of 0.0824 in Argyllshire means that 0.0824% of the people in Argyllshire on census day were called BUIE.
The Index column shows the relative probability of finding someone called BUIE in this county or town, compared with the probability of finding them anywhere in Britain as a whole. An index of 1 means that if you pick someone at random from this county or town, you have exactly the same probability of picking someone called BUIE as if you picked at random from the whole of the UK. Where the index is higher than 1, then you are more likely to find someone called BUIE here than if you picked from the UK as a whole, and where it's lower then you are less likely. The actual figure shows the level of probability - for example, a figure of 2 would indicate that you are twice as likely to find someone called BUIE here than in the UK as a whole, and 10 would make it ten times as likely. The value of 169.02 in Argyllshire means that you are 169.02 times as likely to find someone with the surname of BUIE in Argyllshire than you would be in the whole of the UK.