A method of cleaning a swimming pools comprising;
Having a pool vacuum with a laser range finder attached;
Aiming the laser range finder...
Is it okay to use "Having" to introduce an element like that or do I have to use "a"?
Unclear if you intend this to be a recited step or just setting the stage for the actual steps of the claim.
You need to make each step clear. Often "providing" is used in a step as in "providing a pool vacuum . . . ". That makes it a step. But can be a problem. To successfully allege infringement of a method claim all steps must be performed by a single infringing entity (or another entity directly controlled by the infringer). If the infringer just walks into the pool area and stumbles across the "provided" item maybe they did not do the providing and therefor did not execute that step.
"Using a pool vacuum with a laser range finder attached" might not be interpreted has a step but might just set the stage for the actual steps. Better - ". . . with a pool vacuum having a laser range finder attached, aiming the laser . . . ", would be more clear that no step was being recited until we got to aiming.
Since pool vacuums generally do not have lasers attached you might need to provide some structure information like "where the laser is fixed to the . . ."