Vapor Pressure Deficit

Take a second to learn about Vapor Pressure Deficit. It's actually really simple; it's a simple formula that uses temperature and humidity to figure out the optimal value to get your plants growing at their best. Watch a video about it for more information.

Some source code

You'll need an SHT20 sensor for this one. Load this Arduino Create onto any board and it will print out the current VPD. Refer to a chart to figure out what's ideal.