As a QS which task is most difficult? Estimation? Variation? BOQ? WHY?

estimation is the process of measuring and arithmetical computaiton to come up with a certain result usually in the form of volume or area...this yields the BOQ or the Bill of Quantities...therefore, estimation and boq are almost one and the same. Based on your question of the level of difficulty between estimation/boq vs. variation/change order...i will say estimation is the more difficult of the two simply because it has a wider scope while variation simply taking-off the materials to be added and/or deducted in a single scope of work in a specified area.

Hello

Firstly question to be clearly understood, It says which task is difficult. I could say all the mentioned activities are difficult  as per its scenario, I mean when we talk about variation it depends on what basics we are requesting for variation and type of contract should be a key part. For Lump Sum jobs variation will be easy way if we did it when it compared with tendered documents and Scope of work.

For unit rate and reimbursable it only on some cases we can get variations as per site/Client requirement according with tender documents.

 When we talk about estimation, it is easy way to estimate lump sum jobs. We bid lump sum projects on the basics of drawings specification and vendor list provided by FEED contractor. So we not required to bother about technical stuff. If owner is not confident with design then they will choose to subcon for unitrate contracts which is difficult task to estimate.

When we talk about BOQ, Its is part of estimation and variation

Thank you

Estimation for the most difficult task because if the estimation cost above for project then totally insert for client and company member

Variation part is more difficult. Because the approval is risky. 

For the most difficult task is Variation Because it requires a lot of Processes and Approvals.