This chart is limited to the lowest difficulties in rock climbing, as for beyond the IV UIAA only skilled climbers can go, and skilled climbers do not need explanations.
I = First degreethe easiest climb ... there were all (even the best climbers) must use their hands to keep balance
if you can move without using both hands this is not I degree
Rock quality evaluation skill needed
II = Second degreethe real beginning of rock climbing
movements must be done a limb a time
many holds and grips to choose from
Rope can start to be useful
III = Third degreerock becomes very steep or almost vertical, good holds and grips
Rope teams should move with pitches
a simple comment ...I've limited my chart for some simple reasons :
beyond the IV UIAA only skilled climbers can go, and skilled climbers do not need explanations, they should have tried :)
On the contrary I've seen many not skilled (or beginners) climbers thinking that they're ready for a III UIAA climb after having climbed simple real I UIAA routes, so that they're going to meet some problems and some risks ...
I can remember when, many years ago, while I was leading 4 friends of mine along the normal route of Pizzo Badile (II UIAA), there where 2 rope teams of beginners that went back at the first chimney saying : "this is a hard route, it is at least IV" : the hardest route they had climbed before was the Canalone Porta to Grignetta ...