There's an old saying, "That's like comparing apples to oranges." What it means is that it's sometimes unfair to compare dissimilar objects. I said "sometimes," because at other times it's completely fair. Suppose I hand you one apple and one orange. Which one is heavier? Which one has a larger diameter? These aren't unfair questions, are they?
So sometimes you can compare apples to oranges! And when it comes to your robots, there's a way for your robots to compare things, too—not apples and oranges, but numbers.