Prosperity Production Tools and Critical Rate

Tools like Blacksmithing Hammer of Prosperity give 3% to critical chance. I am unsure if that is shown visually during the process.

Additionally, I am unsure if critical gain is a linear gain as I have <1% on fancier equipment. Is that 3% basically a wash in the negatives, I.E. I have a negative 15% chance of critical and the 3% makes it %12 or is it that I have a ~0% chance of critical and the tool brings it to 3% but doesn't tell me?