 Most of the time, distances measured in the field are assumed to be horizontal distances. If the distance is long or the slope is severe, the person on the lower end of the tape may not be able to hold the tape high enough to bring it to level. If you encounter this situation, then you must break the measurement into two or more shorter measurements so the tape can be held level for the entire measurement length. The measurements for each section are then added together to estimate the total distance measured. This is why it's called breaking tape. When measuring each section, the tape should be pulled taut and straight, not left slack, but not overly tight to the point of excess stretch. If the tape is not pulled tight, all distances will be too long and a positive bias will result.