I also used DRAINC for calculation of SPI, but it gives different values. Please clarify as I have used gamma distribution in DRAINC?

The source code of DrinC isn't available, so, we don't know why does it happen? For finding the difference, Agrimetsoft's team check the mentioned tools by the same input file. So, we checked the MDM, RDIT,... by manually calculation for several stations. For testing an example, you can see SPI's results for Mashhad in attached.

In addition, we calculated SPI for the Mashhad station by DRAINC and It was attached. We find out there was a little difference. Agrimetsoft's software tool (Meteorological Drought Monitoring) works true.

Another way for checking the results is refering to the important center which name is "National Drought Mitigation Center", and run its tool. So, you can compare RDIT and MDM with Drought Mitigation Center software for spi. Agrimetsoft has checked and run the mentioned tools. The achieved results revealed that the National Drought Mitigation Center's tool has presented the same results of SPI as the RDIT and MDM software tools. You can also check the tools for obtaining the results. Just try it?

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