The whole every other diagonal move equalling 10 feet is a pretty good approximation of diagonal distance if you are going to round to 5 feet squares. However it is possible they are using the optional rule to approximate the actual rule. The DMG says that for a more mathematically correct movement, every-other time you move diagonally costs 10 of movement. Given all that background, I believe FG uses the basic non optional rules - but the movement, target and pointer lines are rounded to the nearest 5 feet. And I realized that, although there is information in the Dungeon Master’s Guide (DMG) such as item rarity and function, and tables for randomly generating items found in loot hoards, the thinking behind item design and distribution isn’t very well explained. This is similar to the D&D 3.x movement rules. I’ve seen some people in my various DnD Facebook groups confused about magic item distribution in 5e. In the DMG pg 252 the variant grid rules are expanded upon which some other optional rules, one of which is the first diagonal is treated as 5 feet of movement and the second diagonal as 10 feet and you keep alternating with the 3rd counted as 5 feet and the 4th as 10 and so on. On pg 192 of the PH there is a variant (optional) rule for "Playing on a Grid." This is the 1 space of movement in any direction (including diagonals) is treated as 5 feet we were talking about in some posts. So the base rules work best when - there is no grid at all. Hit Points Hit Dice: 1d8 per monk level Hit Points at 1st Level: 8 + your Constitution modifier Hit Points at Higher Levels: 1d8 (or 5) + your Constitution modifier per monk level after 1st Starting Proficiencies You are proficient with the following items, in addition to any proficiencies provided by your race or background. Anyway, many of these gripes have been answered either. In my still somewhat limited experience this seems to work best with "theater of the mind" encounters which, ironically, are usually less precise. As a monk, you gain the following class features. I have other notes regarding details in the DMG and MM, but I think this answer is long enough already. The base rule for combat is actual distance as explained in the PH on pg 190. Mavrik there are three sets of movement rules in play here.