Project Control Tolerance

you can define and set that threshold in terms of float. ie the schedule falls behind schedule by -20 days then a revised schedule will be requested. If the forecasted cost above the budgted amount by X % then a red flag goes up. If the number of deficencies  reaches a certain % then a red flag goes up and investigation begins as to what the root cause for the deficiencies is and recommendation on how to correct it. 

thanks Zoltan, my question is: Is there a specific rule depends on the size of the project?

best,

muataz

for float it does not depened on a project size 

for cost it does not depened on size

fro quality it does depend on size and you would have to nornmalize the deficencies basd on the size of the project