Checking cue straightness.
You will never see a Professional Player rolling a Cue.
It is an old myth to roll a Pool Snooker or Billiard Cue to see if it is straight, when you roll a cue it will follow the “taper” of the cue, the taper is where the cue gets thinner towards the tip in a cylinder shape, if the roundness in the cue taper is slightly out it will make the cue roll strange.
The Taper of a cue does not affect play in any way.
Option 1. If you wish to check straightness hold the cue up to a window, gently spin the cue looking down from the butt to the tip end, this is called sighting the cue.
Option 2. Place the but of the cue on a slate pool table, rest the joint on the edge of the cushion, gently roll the cue back and forth looking at the tip.
Option 3. (not a true indication) Eliminate 1/2 of the taper, to do this unscrew the cue and gently roll only the Shaft (top section) of the cue without pushing down on the cue.
When Selecting a Cue to purchase please insure you are buying the correct cue for the application. There is no use buying a cheap cue to play competition. Cues are manufactured to a purpose and price.