Well, honey, 6.80 is the same as 6.8, just with an extra zero for dramatic effect. So no, 6.8 is not greater than 6.80. It's like asking if a dollar is worth more than 100 cents - same difference, just different ways of looking at it.
They are both the same because 680mm equals 68cm
680 mm is the same as 68 cm
755 is greater than 680
680 millimetres is the same as 68 centimetres.
68 is greater than 67.
467 is 68 greater than 399
680*1/10 = 68
The same as 10 sixtyeights; 680
1/10 0f 680 is 68
Greater.
680
68 is greater than 34 6/8 is equivalent to 3/4