Vending and parking machines often display the message "no change provided", and retain any payment above the required amount. This is mildly annoying, but we live with it. But it got me asking what the value of this policy is to the vendor. Here is an interactive dashboard that uses random sampling to estimate the value of retaining change across many small transactions.

Following from our earlier conceptual systems thinking diagram, here is a simple working simulation model of a company with a call centre, that takes into account various interrelated factors such as call centre volume, staff retention, customer turnover, and staffing costs. This model runs in your web browser, so you can see how changing the numbers affects the bottom line.

In the run-up to the Copenhagen climate summit in early December, I am dismayed by some of the lax targets being proposed for reducing carbon emissions. Some of the targets sound aggressive because they are expressed as a reduction in emissions. The problem is that emissions is a flow, but we need to reduce atmospheric concentration, which is a stock. Below is a live simulation (the first to be posted here) which illustrates the difference:

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