Tape measures are often used to give a standardized length for objects which are of an irregular shape, like this one.

Rulers or meter sticks are used when the things you are measuring are flat or straight.

The circumference of an object is the distance around it. Since this object does not have a true spherical, or ball, shape, you should measure the circumference of it in two directions. Call one of the measurements the vertical circumference from the "top" to the "bottom", and call the other measurement the horizontal circumference from one "side" to the other "side".

It is important to measure carefully, and record the unit of measurement along with the number you get, because your notes may be used by another scientist in describing or identifying a specimen later on.

First, measure the vertical circumference of the "rock":

Then, measure the horizontal circumference:

Or, if you are done making observations,
you can continue with your investigation...