Help with petroleum engineering HB Vol:1

[HWdubaı]

Hi guys. I am just starting my MSc in Peteng and so I downloaded the first volume of Petroleum engineering handbooks. I am stuck on the 1rst chapter, 1.1 Mathematics of vibrating systems. It basically gives a formula of y=-gt^2/2 and then goes to a depth vs time chart. Anyway then example goes to at 3 seconds the distance is -96.522 ft. This is where I am confused, how did they get that distance because it is not from the chart. Also they say distance at 4 and 2 secs to be -241.305ft and -48.261 ft. How are these calculated as on the chart they are basically incorrect. What forumula is used?? Does the constant g change? Please I am a beginner so give me an indepth explanation as I am really confused.

[HWdubaı]

I see everyone sending and downloading crazy complicated textbooks' SPEs so this has to be the easiest question for you guys. Its the first example on chapter 1.1 of the 1rst volume of petroleum engineering handbook

[exp008]

"at 3 seconds the distance is -96.522 ft" - this statement is incorrect, it should be "at 3 seconds the velocity is -96.522 ft/s". He calculated that by taking a tangent of that point and reading the points from the graph.