If you see/hear "Total carat Weight" aka TCW, that's a different issue. TCW means all the stones on a setting - side stones included.
Okay, back to carat weight and how, at certain points or levels, it affect the price per carat. Prices at these levels often increases significantly. Some of the levels are 0.5 carat, 1.0 carat, 1.5, carat, 2.o carat - well, you get the idea.
As a matter of fact, if a dealer aka jeweler is offering you a diamond that you like at a 1 carat price and your sharp eyes pick up on .98 carat on the cert, you have a good bargaining position.
S/he will probably tell you that that's acceptable in the industry, just smile a tiny little knowing smile and shake your head ever so slightly.
BTW, that's a good tactic when you feel something has been misrepresented but you're not really sure what it is.
Well, bluffing works in poker .. sometimes.
Back to buying engagement diamonds