I need help understanding the % did in T

Table # 2: Determination of the period and frequency of the simple harmonic motion Mn (8) = _50 MT = Mn + Mow Texp 10 MT TT = 3.14 10 VK MSw MT MT t10 Texp Tth % dif in (8) (8) ( kg) * (s) (s (S T 200 250 0.25 11.2 1.12 1.08 3.93 220 270 0.27 11.7 1.17 1.12 4.47 240 290 0.29 11.8 1.18 1.16 1.67 Frequency when Mew = 200 g. 1 Note: fexp - Texp 0.893 Hz Mh: Mass of the weight hanger tio: Time for 10 oscillations Mew: Mass of added slotted weights Texp: Experimental period Mr: Total Mass Tth: Theoretical period fexp: Experimental frequency