With the rough rule of thumb, the 3rd in 2018 would be worth a 4th this year. From what I understand, most teams use their own internal chart that vary slightly from the one posted here.
Also, it's very important to understand that each draft is different and results can vary wildly depending on who is available. For example, there is no way you were trading into the #2 spot for the Luck/RG3 draft like Chicago did today. It took a king's ransom to get that pick because of the players involved.
The naysayers can point out the aberrations, but for the most part the draft chart is still very much alive.