How do you calculate the number of ridge unions required?

The number of ridge unions required is not the same as the number of ridges, for instance if you were using 50 ridges to fix along one ridge, there would only be a need for unions at the point where two ridges meet, in this case 48 unions would be required. 

Where the ridge meets the end of the ridge line, and end cap will be used or that ridge will be replaced with a block end ridge. 

It is also worth noting that the unions and end caps constitute a mechanical fix, due to BS 5534 specifying that each ridge tiles requires two mechanical fixings.