Limitations 

There are many variables that affect the results and a fluctuation of any of those that I am controlling will result in incorrect, biased or anomalous results.
The factors that are most likely to cause inaccuracies are:

• The accuracy to which I can dilute the hydrogen peroxide, including; drips, pipettes leaving different amounts in the tip, parallax error (minimal), gradual breakdown of the hydrogen peroxide and impurities in the beaker including water (after being washed out).
• The accuracy to which I can control the surface area of potato exposed to the hydrogen peroxide including; the accuracy of the scales, water on the potato cylinders, the temperature in the room (the borer expands with a rise in temperature, affecting the size of the cylinders), although only a minor consideration, the way in which I trim the cylinders to have the same weight and the density of the potatoes (which could change due to incipient plasmolysis).
•    Fluctuations in the precise set-up of the apparatus, including the depth of the water in the ice-cream tub (which affects the pressure which the oxygen has to push against), the relative heights of the beaker and the bottom of the burette and the air pressure on the day. I think that using two experiments set up at once (obviously can’t be identical) was a major cause of this error. This could have been the primary cause for the fluctuations at 12.5% and 15%.
•  The accuracy of the measurements including; the time lapse between seeing a bubble get to the surface of the water in the burette and stopping the stop clock and the size of the bubble .
•  The accuracy to which I can measure the temperature, the time lapse between finishing the reaction and taking the measurement possibly being significant because the reaction is endothermic and the hydrogen peroxide is kept in the fridge, therefore the solution will get warmer the longer one leaves it until it is at room temperature.  The thermometers to which I will have access are also not very accurate.