No single system or process exists for creating accurate estimates on a technical project.
If you look in the metaphorical toolbox of any seasoned project managed worth their job title you would find a variety of methods that will let them zero in on an as accurate an estimate as can be established for that series of tasks, given the data at hand.
There’s no shortage of people selling silver bullets either from the latest fad method to software costing a significant portion (per year) of a decent project manager’s salary.
There are four keys to bear in mind when estimating on a technical project.
The first is to not rely on a single system of estimation.
The second is understand there are no silver bullets for estimation.
The third is to re-estimate as the data and metrics change and new information comes to light.
And the fourth is to apply the proper estimation method for the current phase of the project.
That latter point is the hardest to teach and the hardest to learn unfortunately from top-down (and also bottom-up) estimation to phased estimation to simulation estimation and parametrics.