This paper revises Swiss GDP emphasizing the difference between single and double deflation, which depends on trading gains: i.e. gains from terms of trade and from the real exchange rate. These gains contributed significantly to Swiss economic growth between 1930 and 1990. Earlier series of Swiss GDP have neglected trading gains. In backward projections, this leads to overestimation of GDP (per capita) levels. The Maddison database (Bolt & Zanden 2014), for example, suggests that Swiss GDP per capita was 38 percent above that of the USA in 1875. My series shows that Swiss GDP per capita was still below the Western European average.