Not tough if you know SI!

It's a grid full of little tricks and red herrings which I like. I felt good about solving it. But there are a fair few possible SI units in the Physicist category (eg Ohm) and most of the SI units are named after Physicists (eg Newton) , which means there are quite a few possible solutions, and it was only through luck that one could find what you've deemed the "correct" one

To clarify, having played a second time, any one of Henry, Newton and Pascal could easily be switched with Ohm to make two groups with the same relations. This is a big flaw in an otherwise very good grid.

In a sense , the highest quality grids are the easiest. If the connections are forced, it is more difficult to work out the answer needed.

I disagree with Mr A. Surely, that is the point of the concept of "red herrings". I liked this grid, didn't get all the answers in the time, but thought it was challenging; and I liked the fact that "Henry, Newton and Pascal" could trip me up.

Grids should only have one logical solution, knowing all the clues. There can be red herrings that fit into more than one category but in the final solution no two answers sjlhould be interchangeable.

I agree with what has been said. Red herrings are expected, but on this grid there are 8 famous scientists! (including Darwin\0.

There is only supposed to be 1 solution. Red Herrings are an essential part of this game, and are what make it interesting.
However, if 2 from one grid can be swapped with 3 from another, this leads to a minimum of 6 correct answers, and defeats the purpose of trying to solve something that is meant to be unique.