Also, this is how mental arithmetic is taught in modern elementary schools! Lots of focus on "ten friends", and performing addition and subtraction by splittin

Also, this is how mental arithmetic is taught in modern elementary schools! Lots of focus on "ten friends", and performing addition and subtraction by splitting into parts to make "ten" and then adding or subtracting the leftover: 8+5 = 8 + (10-8) + 5 - (10-8) = 10 + (5-2) = 10+3 = 13 13-5 = 10 + (3-5) = 10 + -(5-3) = 10-2 = 8 The weird parts of Roman numerals is the lack of clear place value separation (no spacing, variable-length places I, II, VIII, etc), and using 5 V and 10 X so 2 different scales for place value, and the asymmetry of I,II,III,IV, V instead of the more consistent I,II,IIV,IV,V, and using relative position for sign instead of an explicit negative sign symbol.