8. Using weights labeled $1, 2, 3, 15, 40$ grams each, on a balance scale without graduations, if weights can be placed on both sides of the scale, then the maximum number of different gram weights (positive integer weights) that can be measured is $\qquad$ kinds.
8. 55 Detailed Explanation: Using weights of $1,2,3$ grams, all integer gram values in the interval $A=[1,6]$ can be measured. After adding a 15-gram weight, the measurement range expands to the interval $B=[15-6,15+6]=[9,21]$. Adding a 40-gram weight further expands the measurement range to three intervals: $C_{1}=[40-6,40+6]=[34,46], C_{2}=[40-21,40-9]=[19,31], C_{3}=[40+9,40+21]=[49,61]$. However, intervals $B$ and $C_{2}$ overlap by three integers, so the total number of distinct integer gram values that can be measured is $6+13+13+13+13-3=55$.