Saved my bacon about 5-6 years ago, the company we where going to depend on to do a whole bunch of complex calculations related to solar insolation discontinued

Saved my bacon about 5-6 years ago, the company we where going to depend on to do a whole bunch of complex calculations related to solar insolation discontinued their API but didn't tell anyone, I found out when I rang up to get a price. So suddenly I was in the situation of dealing with maths that was harder than anything I'd done at school years and years ago. In the end I transliterated the equations into sage, checked the results carefully and then wrote the PHP to do the same calculations using a large set of tests against the official stuff, stressful two weeks but sage was useful as hell.