Hi Bruno,
First, to avoid any confusion, please note that in an agile context, « value » usually means « business value », which is the outcome of the project = how valuable your product is for end users, stakeholders, customers etc.
Here it rather seems that you want to evaluate the cost of a sprint. The team is expected to be quite stable so the global cost of a sprint can be approximated from the team composition and the duration of a sprint.
In order to be more precise and account for variations within a sprint, you may record individual time spent on a sprint by each team member on a daily basis through a feature called « Team capacity ». As you may have noticed, iceScrum behavior can be extended through Apps. This feature is provided as an App: https://www.icescrum.com/documentation/availabilities/. It allows taking into account variation of team size, holidays, sick leaves, part time, etc., to calculate the time spent on the project both individually and for the whole team. The time spent is entered manually, it is not consolidated from task data.
Regarding data recorded on tasks, by default only the remaining time is recorded, which does not allow to know the actual time spent (e.g. you may think that 8 hours of work remain on task, then work 2 hours on it only to find that only 1 additional hour of work is required).
However, you can use an App to enter the time spent on tasks in a dedicated field: https://www.icescrum.com/documentation/time-tracking/. It is not consolidated in iceScrum but you can use the REST API to collect this data and externally sum the time spent for each deliverable. Here is the documentation of the API : https://www.icescrum.com/documentation/rest-api/. The corresponding task field is named « spent ».
