Enter the path — or an environment variable, in the format ${VARIABLE_NAME} — where an Android SDK installation can be found.
If you want to create emulators on-the-fly, this SDK installation should have one or more platforms installed (check the "platforms" directory, or the Android SDK and AVD Manager).

If nothing is entered here, the Android SDK tools (under the "tools" directory) will be presumed to be available on your PATH.
Otherwise, this plugin will search for an SDK installation under the following environment variables on the build host: