Biology aqa ISA Help?

i need some help on my bio ISA, we are testing if the concentration of mouthwash changes the amount of bacterial colonies in agar jelly, obviously we found the higher the concentration, the less colonies, but what type of variable is the different concentrations? we went up like 0cm cubed, 1cmcubed 2cmcubed and so on till 5 cm cubed. is it discrete because its whole numbers? anyway thanks, a little note on variable would be helpful too thanks .