The term translated here as “measuring rod” is literally a reed.
This reed could be used for a variety of purposes, such as thatch for a roof, a fishing rod, the shaft of an arrow, and in construction as a rod for measuring. (A string could also be used for measuring; the tool John received could not be rolled up but was stiff, “like a [shepherd’s] staff”.)
1 Then I was given a measuring rod like a staff, and I was told, “Rise and measure the temple of God and the altar and those who worship there,