In order to create the ideal environment for your cultivar, it is essential to be able to accurately measure it.
Humidity and Temperature
There are many generic humidity and temperature sensors that are cheaply available. Some connect to a smartphone via Bluetooth and provide a graph of data while others incorporate a smaller LCD to display current readings
Light
pH
When mixing concentrated liquid nutrients with water it's important to ensure the nutrient mix has the correct pH before applying to the cultivar so that it can make use of the nutrients. see also: nutrient lockout