The delay values of IC will varies in different conditions like changing in processor,voltage,temperature(PVT).The delay value of IC in cold weather is different and in hot weather is different.In cold weather the metals in IC will shrink.In hot weather the metal will expand so the delay will increase.To over come this effect flat derate(delay) is applied in the circuit.
In simple words OCV is a technique in this flat derate is applied to make faster path more fast and slower path more slow.Delays varies across a single die due to PVT(processor,voltage,temperature).This need to be modeled by scaling the coefficients.
CRPR (clock re convergence pessimism removal):-
In this concept we removes the pessimism and derate to the common path.Generally we add the delay to every buffer in the process of OCV. But adding more delay is also effect the speed of the chip and it may cause violations to over come this we are removing the delay to the common path in the process of CRPR.
In simple words It can be used to remove the pessimism and penalty by using common cell for both launch and capture flip flop.
physical design: What is OCV and CRPR