Janet Smart

By Janet Smart

Backlog ready reckoner

In a previous blog, we saw that the total number of minutes required to create a catalogue could be estimated. In this blogpost, we’ll estimate the number of person-years required to clear that backlog.

We need to estimate the number of minutes a full-time cataloguer has available in a year. Let’s suppose they work for 48 weeks of the year, and five days per week. We’ll assume, perhaps optimistically, that they work on cataloguing for seven hours each day. The number of minutes available, optimistically, is therefore:

Minutes per person-year = 48 * 5 * 7 * 60 = 100,800 ~ 100,000

We’ll approximate the number of cataloguing minutes per person-year as 100,000. This is probably still optimistic, but it’s a reasonable place to start, because it makes the calculations easy.

Now, we can estimate the number of person-years, P, to clear the backlog. From a previous blog, we know that the time required to catalogue N items is T = Nt . Therefore, the number of person-years to clear the backlog is given by:

P=T/100,000 = Nt/100,000

For very large backlogs, and these do exist, we can simplify this a little more by estimating N, the total number of items, in millions. So, N is actually M million items. For example, instead of N = 3,000,000, we use M = 3.


Cancel through the 1,000,000 against the 100,000 to get 10, and we find:


For example, if a museum had a backlog of two million items, and it estimated that each entry would require 10 minutes of work, then the number of person-years required to clear this backlog would be:  years. Thus, this backlog would take 20 hard-working people at least 10 years to clear.

Another way to look at this is to re-arrange the equation slightly to make t, the amount of time per entry, the subject of the equation.


Now, suppose a museum has a backlog of 4 million items  ( M = 4 ) and they have been awarded funding sufficient to pay for four people for five years. This would mean that P = 4 * 5 = 20. Therefore, the time available to catalogue each item would be

equation for backlog ready reckoner post

Thus, the project would only allow this team of cataloguers, at most, half a minute on each item.

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