TOPIC: Question regarding the Project Time & Cost Management

While I was reading the PMBOK guide (5th), two contradictory ITTO diagrams between "6.4 Estimate Activity Resources" process and the "7.2 Estimate Costs" grabbed my attention, and it doesn't seem to be logical to me.

In 6.4, Activity cost estimates is an input to the "Estimate Activity Resources", which will be used for developing "Project schedule"; while in 7.2, Project schedule is an input for "Estimate costs" and the output is "activity cost estimates". How come these two things serve both as input and outputs to each other? I have a hard time understanding the logic here. Please advise.

Thank you so very much!
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Kindest regards,

Kelly

Just because "Activity Cost Estimate" shows up twice does not mean it is the same estimate, e.g. the first estimate used as input to the project schedule might get re-evaluted in the "Estimate cost process" and result in a revised Activity Cost Estimate.