What to consider with first stages First of all we have to distinguish between unbalanced and balanced first stages. Unbalanced first stages decrease the intermediate pressure (that affects the performance) while lowering the pressure in your cylinder during the dive. Balanced first stages are not affected of the pressure in

When it comes to the definition any dive 300m higher than sea level is considered as an altitude dive. However, living in an alpine country such as Switzerland we redefine this a bit.