 So I'm going to give you the rules for determining how many significant figures a number has and then I'm going to show you how they work. Here are the rules. Make sure you have a copy of these in front of you when you move on through this video. It'll help you to understand the examples. First rule, all non-zero digits are significant. In the number 23 you have two non-zero digits, two and three. Clearly both of those digits have been measured. So this number has two significant figures. Second, all captive zeros are significant. Captive means zeros that are between other non-zero digits. So in 203 and in 4.089 the zeros are captive. They're between non-zero digits. So both they and the non-zero digits count. Hence 203 has three significant figures and 4.089 has four significant figures. Third rule, leading zeros are never significant. A leading zero is a zero at the front of a number. This could be either a zero in front of a whole number like in a big digital display that counts upwards, or it could be the zero in front of a decimal number less than one. Either way the function of these zeros is only as placeholders. They tell you nothing about the accuracy of the number. So 00807 which is 807 has three significant figures and 0.53 has two significant figures. Fourth rule is to do with trailing zeros, but there are two possibilities here. In numbers where there is a decimal point trailing zeros are significant. This is because if a decimal point has been specified then we know that all of those digits have actually been measured. If they hadn't they wouldn't even be written down. So 160.00 has five significant figures because all of those zeros were actually measured. And 0.9140 has four significant figures. Remember the leading one is not significant. However, in numbers that have no decimal point trailing zeros could mean that the number has just been rounded off. So they're ambiguous and we treat them as non-significant. So 3500 we treat as having only two sig figs.