The Global Calculator online tool is controlled using a series of levers that represent changes we could make that would mitigate against climate change from now until 2050. There are 14 "grouped levers" which drive activity in different sectors. These can be expanded into around a total of 40 main "levers" for more detail.
For each lever you can choose different levels of effort – for most this will range from level 1 (make minimal effort to tackle climate change), to level 4 (make an extraordinarily ambitious and extreme level of abatement effort). Every time you move a lever, you can see the impact it has on energy demand and supply, emissions, the climate, resource availability, and many other factors by looking at the graphs on the various tabs.
For more information, download Level 1 to 4 definition.pdf.