Can someone help me find acceleration using the slope and the percent error for this chart

A C D Length (m) Time f for 10 complete oscillations (s) Period T (s) Period squared T^2 Period squared T^2 theoretical 0.80 12.23 1.2230 1.4957 1.0258 Period squared T^2 vs. Length (m) in Oscillations Lab 0.70 11.49 1.1490 1.3202 0.8976 0.60 10.21 Period squared T*2 - 1.84x . -1.93E-03 1.0210 1.0424 0.7694 0.50 9.50 1.5000 0.9500 0.9025 0.6411 0.40 8.25 0.8250 0.6806 0.5129 0.30 7.87 0.7870 0.6194 0.3847 1.0000 10 Line of Best Fit Slope Acceleration Percent error Period squared T^2 11 1.28x+4.59E-15 1.28 12 0.5000 14 15 0.0000 16 0.30 0.40 0.50 0 60 0.70 0.80 17 18 Length (m) 10 20 21