PHP Volume Calculator: Perform calculations on volumetrical materials

This class can perform volumetric calculations on materials used in the laboratory flasks, micro-pipettes, etc.. Currently it can:

- Generate codes for volumetric material and generate random codes for the calibration
- Get ambiental conditions with the API openweathermap.org
- Get water density for any temperature
- Get air density for any temperature, humidity and pressure
- Get volume to a 20ºC for corrections
- Get the coefficient of cubical thermal expansion for different material
- Get the maximum error for micro-pipettes, burettes and other piston volumetric material
- Get the uncertainty for the calibration of volumetric material