"the key to determining" is a correct and usable part of a sentence in written English.
You can use it when you need to describe something that is necessary to achieve a certain outcome. For example, "The key to determining the validity of his claim is to look at the evidence he has provided."
Taking the pulse is the key to determining your dosha.
We had found the key to determining a good workplace: ask the people who work there.
That is important to know, because it will give you the key to determining the right inventory level.
The key to determining just how much you should be lifting, he continued, is gauging your point of fatigue.
The key to determining whether a person receives help will be a so-called net present value calculation by the mortgage company.
Such tests are the key to determining the strength of the material used in reinforced concrete buildings, according to Vincent J. DeSimone, the chairman of DeSimone Consulting Engineers.
That will be the key to determine the profit outlook for banks," she added.
The following lemma is the key to determine these intervals on real axis [15].
The determination of the metastability condition in fluid flows through singularities (expansion devices) when flashing occurs is the key to determine the mass flow rate going through devices when there is a great pressure difference between upstream and downstream.
Sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface.
"If Henrietta Leavitt had provided the key to determine the size of the cosmos, then it was Edwin Powell Hubble who inserted it in the lock and provided the observations that allowed it to be turned," wrote David H. and Matthew D.H. Clark in their book Measuring the Cosmos.
