Measuring stuff or drawing a straight line.
a ruler is used to measure inches or 1 foot
A ruler.
measuring scale, tape, or ruler is used.
Ruler
Jim used his ruler to measure the length of his finger. Bob is the ruler of the world.
The answer depends on the graduations marked on the ruler.
A ruler is used to help us measure things.
the ruler was used to measure the length of my book.
Measuring things
Ruler
nothing
They used a ruler.