What is the length of the gray object assuming the other end of it starts at zero. Make your measurement as exact as possible.
In your guess for its length, the 10's place is known with certainty. The object is at least 20 units long. The number in the 1's place is now known to be at least 9 units long. The tenths decimal place is now known with certainty. It is 0.2. This time a new digit is unknown, the hundredths decimal place. It is an estimated measurement of 0.3.
How do you find the estimated number in a measurement when using a ruler or other scaled instrument?

Sometimes, a ruler, or device with markings on it, is not shown, and yet the precision of the measurement still needs to be determined. There are rules for determining the precision of a measurement and how to do math with these measurements' various precisions. Here are some examples
of significant figures in the life of a consumer.
This is a memory storage card called a micro "SDHC." The label lists its storage capacity as 4GB. That's 4 000 000 000 bytes of storage space. Actually, that's not completely true. Following the rules of significant figures the "4" in "4 000 000 000" is actually an estimated number. This card actually has 4 294 967 296 bytes of available space. In this case the "4" is a rounded number. 

This is the bottom of a sugar container. It says the package holds 1 pound and 4 ounces of sugar.(Look to the right at the bottom.) The "4" is an estimated number. This means it could hold 3.5 ounces of sugar or 4.4 ounces of sugar. (In reality the label does not tell the whole significant figures story. There is a government agency that over sees the accuracy of the label. It is much more precise than plus or minus a half ounce of sugar.) In the state of Virginia it is the agriculture department that goes around to make sure that the amount of gas you pump into your car is what the gas pump says it is. they also check to make sure that when you buy produce by the weight, the scales that produce is weighed on is accurate. (You don't want to be over charged because the scale is not accurate.) 

