If you have no weather-station then Weather-Display may not work for you because it normally expects to be getting weather data, especially barometric pressure, which it validates as being reasonable before recording any data.
How important is calibration to you? How accurate do you need the data to be? Answering those questions will help determine the best solution, because to get a scientifically accurate result you would need to start with an accurate sensor, both electronically and optically.
Please tell us more about what you are trying to accomplish and we can help you better.