This was really inconvenient topic to google out - so I'm asking for clarification, did I understood things correctly.
I'm talking about measuring short distances in Mercator projection (3857). You can calculate distance in map units (using Pythagoras theorem). In equator, it equals to distance on earth (scale factor = 1); if you move towards poles, distance in map units and in earth are not equal anymore - scale factor starts to increase.
Question is: how to calculate scale factor for given latitude?
Did I understood correctly, formula is
factor = 1 / cos(latitude)?