Cultivating cannabis involves such an wide range of variables that influence its growth, flowering and yield, that regular control of how things are going on is necessary.
One of the most important thing to measure is the feed pH - it should not, under any circumstances, be too low or too high, as it might severely damage or even kill your plants. Since it is close to impossible to judge, whether the water is acidic (ph 7), you might want to use a pH meter.
If you are using hydroponics system, you will also certainly need an EC meter. Electroconductivity (EC) basically tell you how resistant the water solution is to current, implying the amount of nutrients. Hydroponically cultivated crops are highly sensitive to EC changes, so you will need to keep an eye on it.
Almost all of the standard equipment in your grow area (light and, ventillation in particular), will also need another sort of control - over their work schedule. Being an indoor cannabis farmer you take up the responsibility of setting the time when the lighting should start, and when to cool down, when to turn the ventilation on and off etc. - all that can be done by either mechanical or digital timers.