 Okay, this one is actually a very difficult concept for introductory chemistry students to get correct and that's to use the measuring devices to give you the correct measurement to the right number of significant digits. So, I think it might be easiest to go over here and start with D. And you can see the graduations here are for every 10 milliliters. So, in between that, we have to estimate. So, when we look at this measurement, right, we're looking at the bottom of the meniscus there and it looks to be about 64. I don't know. It's hard to tell. I don't know if it's 64, 65, 63. Because why? Because we don't have those graduations here. So, I have to make my best guess as to what that second digit will be. In fact, that brings to mind another topic we've talked about is that this, the first digit here, the 6, that's a certain digit and the 4, that's uncertain. We're not really certain of what that is. This measuring device is not very precise. So, we've got to keep that in mind. Okay, so with that thought process down, we've got to go, or let's go to A over here and we see that now we do have those graduations in between the 10 milliliters. It can be more precise with our number that we're measuring. So, if we look at where the meniscus is here, it's somewhere between 54 and 55. So, I'm sure that the measurement is 54 points something. So, these two numbers are certain. This last digit, that's estimated. So, it's uncertain. I'm just going to say, because it's hard to tell there 54.5 mills. Okay, remember to put your units there because your answer needs both numbers and units every time you're doing an answer. So, let's go ahead and look at this thermometer. So, it's the exact same strategy we used back here because we have graduations in between the 10 degrees, each 10 degrees. So, we can go 41, 42, 43, et cetera. So, we know that it goes up to 48 and I don't know how far it goes, but it looks like higher than 48.5. So, I'm going to estimate that last digit to be 7. Okay, and then we got to put our units, which is degrees Celsius. And then lastly, we'll look at this C, this thermometer in C, where you can see here the 100th digit has been graduated for us. Okay, so the 10th digit has been graduated for us, so we can go to the 100th digit with our estimation. So, we see that it goes up to 46 here, and then if we count these, it's past 8, but not quite to 9 yet. So, I'm going to just put a 5 there. It's hard to see. So, 46.8, all those digits are certain. The 5 is uncertain. So, when we talk about significant digits, this first measurement has three sig figs. This second measurement has three sig figs. The third measurement has four sig figs. The fourth measurement has two sig figs. And every one of them has only one uncertain digit, because that's the one you have to estimate. Okay, so hopefully this makes sense. This is a really good problem, I think, and it's, like I said, very difficult sometimes for introductory chemistry students to get this correct, especially when they're in the lab. Okay, let me know if you have any issues with it.