Line up the zero mark on the scale you are using with the beginning of the item you are measuring to start using a scale ruler, according to GEI International. Then, determine at what point on the scale the end of the item is, and read the number on the scale closest to that point.
Keep in mind that this number should always be rounded down as it represents the whole feet of the item you are measuring. Next, slide the ruler so that the number you read lines up with the end of the item. The fractional feet to be measured is then represented by the distance from the beginning of the item to the zero point on the scale. Add this reading to the number from earlier to get the full measurement of the item. It is important to know the scale of the item being measured so that the correct scale can be used when measuring with the ruler. For example, 1/8 on the ruler is a scale that converts 1/8 inch to 1 foot. There are also two scales on each edge of the ruler. One scale reads left to right, while the other reads right to left.