Or to leave it to an electronic brain?
Despite all the negativity you read about relying on your Smart’s ECU to do the job for you, that’s just what I do. Nearly always. When you start from cold though it’ll hang on to first for dear life (or about 4,000 rpm) and if you go up a steep hill relatively slowly it’ll tend to chop and change between gears. So, a bit of DIY at those times.