I have a little bit of difficulty with this formula here,

If order of magnitude spread is -50% to +50%

And the actual cost of project is $100,000
Then 50% of it is $50,000

So the range will be $50,000 to $150,000,

However on some prep material that I have found, a project with target price of $100,000, has a range of  $75,000 - $175,000 with this level of estimation. Is this because anything higher than %50 i.e. 75% is also considered rough order of magnitude?

Please help me understand this.