Final answer:
The precision for a measurement of 18 (1/2) ft is given by the smallest possible increment among the provided options, which is ±1 inch.
Step-by-step explanation:
The precision of a measurement indicates the smallest increment to which the measurement is reliable. In this case, we are trying to find the precision for a measurement of 18 (1/2) ft. The options provided are various increments by which the measurement could possibly vary, such as ±1/2 ft, ±1/4 ft, ±1/8 ft, and ±1 in.
In determining precision, we must consider which option represents the smallest increment of measurement variance. This means we are looking for the smallest unit among the options provided. Here, an inch is the smallest unit, so ±1 in would indicate the most precise measurement, given that there are 12 inches in a foot, making it a smaller subdivision of a foot.