Well, bobpursley explained this to me. I didn't understand this well. Since there was an error in the data, I am posting it again

Question

t(sec) v(ft/sec)
1 12.2
1.5 13
2 13.4
2.5 13.7

velocity of an object moving along a line at various times.
How do I estimate the object's acceleration(in ft/sec^2) at t=1

TIA

acceleration at t=1 estimate

delta V=13-12.2
De;ta T= .5

that is the deltas between t=1, and t=1.5

acceleration=deltaV/deltatime