 So let's do another significant digit problem. So here's another measurement that we found in lab. So 2005 centimeters. And we want to look at, well, try to figure out how many significant figures there are, how many certain digits, how many uncertain, and what are the units, OK? So can anybody tell me any of these things? More centimeters. The units, OK, centimeters, Zm. So remember, every time you have a measurement, you've got to have units, OK? Because it's just as important as the number, because you don't know what the units are. You could ask, well, is that meters? Is that miles? Is it tons? Who knows, right? So centimeters, metric or not? It is metric, OK? So circle arguments. Anything else that you guys can help me out with this one? OK, four significant figures is what I heard, OK? Four significant figures. Is that correct? You guys, I agree with that, OK? So that means, so how many digits do we have all together in this number? Four, right? So that means every one of those numbers that you see in our digits in this particular number is significant. Is everybody OK with that, OK? So how many uncertain digits do we have? One, always, right? So we must have how many certain digits? Three, OK? So why do we say that? Because our significant figure calculation tells us that it's certain digits plus uncertain digits, right? And uncertain digits, what do we say is always one? And if we have four significant figures, so we could do something like this, let's rearrange this equation. Certain digits must be 4 minus 1, which equals 3. Can everybody rearrange that algebraically, OK? So if you can't do that, try to do it on your own, OK? Come to me after class or something like that if you're having trouble with it. OK, so which one is the uncertain digit? Is it the 2, the 0, 0, or the 5? The 5. Why would you say the 5 is the uncertain? It's the last one, OK? That's the one that's, you know, if it was on a balance or something, it might be going back and forth between 5 and 4, or, well, on this measurement. You don't know exactly. It's coming in between the graduation. So that's the one you have to estimate, OK? So that's the uncertain one. Does everybody understand this particular problem? What type of zeros do we have here? Captive zeros, right? So captive zeros always what? Significant, right? They're always significant, OK? Captive zeros always significant. Always in between those ones that you said always significant. So are there any questions on this particular type of problem? OK, wonderful. You guys are doing awesome tonight. I'm proud of you.