From the title, I thought it was a repost of something I had seen before, but it's not. What I was thinking of was "Accounting for Computer Scientists" [1], which explains double entry book keeping and profit and loss statements and balance sheets by formulating them in CS terms (directed graphs with accounts as nodes and transactions as edges). It was discussed on HN [2].
[1] http://martin.kleppmann.com/2011/03/07/accounting-for-comput...