Asking about resistors for a FreeTrack IR clip
The SFH485P I.R. diode is capable of taking current continuously up to 100 mA. It also has a forward volt drop of about 1.4 volts when this current is flowing. If your power supply is 3 volts then you need a resistor than can drop 1.6 volts at 100 mA. Ohm's Law tells us the resistor should not be smaller than 16 ohms. Given the ones recommended are 30 ohms you will get slightly less light output using a 33 ohm resistor but this may not be a problem.

Alternatively use 27 ohm resistors as you will be a long way from exceeding the 100 mA limit current but, battery life will be less.