How to measure ozone output of an ozone generator using chemical methods
You can do the quantitative estimation of ozone ($\ce{O_3}$) by two reactions. First one is the reaction between $\ce{O_3}$ and potassium iodide ($\ce{KI}$), and the second one is an iodometric titration.

First, ozone is reacted with excess $\ce{KI}$ in presence of borate buffer ($\mathrm{pH} =9.2$), and due to this reaction, iodine ($\ce{I_2}$) and oxygen ($\ce{O_2}$) are liberated as follows, $$\ce{O_3 + 2KI + H_2O -&gt; I_2(^) + O_2(^) + 2KOH}$$

Now this mixture of gases is passed through potassium pyrogallete solution, which absorbs $\ce{O_2}$, and we are left with $\ce{I_2}$. Next, this liberated iodine is dissolved in a solution to make a particular volume, and then titrated with sodium thiosulfate ($\ce{Na_2S_2O_3)}$ of known strength in the presence of starch indicator. 

$$\ce{I_2 +_ 2Na_2S_2O_3 -&gt; Na_2S_4O_6 (sodium tetrathionate) + 2NaI}$$

At the end point of this titration, colour of the solution turns colourless from blue ($\ce{I_2}$ + starch gives blue colour complex  which is lost at the end of this reaction).

So, thiosulfate reacts with iodine in a quantitative manner, and from there you can determine equivalents of $\ce{I_2}$ = equivalents of $\ce{Na_2S_2O_3}$. Thus, you can calculate what equivalents of ozone had produced that much of $\ce{I_2}$, and also the grams of ozone present.