nail down

Whether that has had the projected effect is uncertain; reams of law-review pages and financial analyses have been filled with conjecture, but it’s hard to nail down the effect.

It took weeks for doctors to nail down the diagnosis.

"I think if we can nail down these negotiations and move towards these negotiations... then the president will take a hard look at lifting this pause," he told Fox News.

“I think it's hard to really nail down.”

Favouritism and nepotism thrive, it's hard to nail down or pinpoint but if you are friends with the right people it makes you untouchable.