We try our best to provide accurate information. But nothing on Earth is 100% accurate and you should keep this in mind while reading the text. The reality is not guaranteed to meet your expectations.
We have run many rivers ourselves, but not all of them, obviously. Those that we did are marked appropriately and provide first-hand information. Other rivers descriptions are compiled from other peoples' reports, taken from libraries, internet or personal contacts. These descriptions may be less accurate, just because we interpret someone else's opinion. To be more informative we add pictures wherever available.
Rivers grading conforms to the commonly used international system (class 1 to 6). Numbers suffixed with "+" or "-" (like 4+ or 5-) mean more or less difficulty than typical for this class. Number in brackets (like 4(5)) means the river is generally class 4, while there are some rapids/sections of 5 which can be portaged if necessary; so class 5 paddling level is desired, but not required. "Loose" grading (like 4-5) means we're uncertain about the difficulty; expect anything in this range.
We have been paddling in many places around the globe, with peoples from different countries, and thus we probably interpret river difficulty in a common way. Nevertheless, bear in mind that everyone's personal understanding slightly differs; after all let's hope you'll never find a class 5 river where we wrote class 3 or vice versa. The classification counts solely technical difficulty of the river or section, you should add environmental factors (climate, accessibility, wilderness etc) as an extra.
Also note that whitewater activity was very popular in the USSR (mainly using catarafts) and thus a "Russian" or "Soviet" grading system formed here, still widely used among catarafters. This system is also 6-step, but less strict (subtract at least one grade to get international class) and often very confusing, there are class 5 rivers with nearly no rapids at all (just very remote) or class 3 rivers containing extreme technical sections (just very short and along the road). When talking about Russian rivers always check which grading system is used.