The Cowboys and many teams use a tiered grading system. I think they divide round one into 3 parts. A player can be R1T1, R1T2 or R1T3. When they are on the clock, they look at the players available on the highest tier. If there is more than one, then they use "need" to make the decision or they might try to trade down if there are several on the same tier. There are some occasions that they will go down a tier and skip a higher tier player, but they try really hand to avoid doing that. If a RB is the only player on the top tier in this upcoming draft, they will likely check to see if any team wants to trade for that player. If not, they will likely drop down a tier because the investment in another RB would be too much both in terms of the pick and the salary.