I'm trying to set up a campaign and I'm not great at math. We play old school 1e AD&D.
The 1e DMG gives two tables on page 47 for chance of an encounter. The base chance of encounter depending on population density, then a matrix of when to check based on terrain type.
For example in a "relatively dense" population the base chance is "1 in 20." In "plains" we are instructed to roll morning, evening, midnight.
Does "1 in 20" mean that if I roll 1d20, there's an encounter every time I roll a 20, or a 1?