What amounts do you compare when measuring concentration?

Related questions

• How do you measure concentration from absorbance?
• How do you measure concentration of a solution?
• How do you measure concentration of CO2?
• What concentration measure changes with temperature?
• How can I measure the concentration of salt in water?
• How is the concentration of a solution measured?
• How does the concentration of electrolyte affect an electrochemical cell?
• How does normality differ from molarity?
• What is the molality of a solution of 10 g NaOH in 500 g water?
• What are the mole fractions of the components of the solution formed when 92 g glycerol is mixed...