What would be the independent, dependent & constant variables in an experiment based on determining the molar conc. of HCl by titration with NaOH?

Experimental
variables can fall under three different classifications, independent variables, dependent
variables, and constant (or control) variables.  An independent variable is one of the input
variables.  In other words, it is the measurement being tested.  A dependent variable is one of
the output variables.  In other words, it is the effect being measured.  Control variables are
variables other than the ones being directly tested.  They may have an effect on the experiment
but since they are not being tested they are held constant to minimize affecting the
experiment.  In the case of titrating a solution of HCl against a solution of NaOH, the
independent variable is the concentration of the NaOH solution that is being added (the input
factor).  The dependent variable is the concentration of the HCl solution (the variable being
measured).  A constant variable would be the chemical indicator being used (like
phenolphthalein).  Since the effect of this is not being measured, it should be kept the same
throughout the experiment.