please sir...can you clarify me the point pleasehow can we mesure...

As mentioned in the methods, there was no normalization needed. Only Ct values were taken into calculations. I suggested about normalization using circular GAPDH only if you want to the real amount of linear RNA (GAPDH) left after RNase R treatment. RNase R is very efficient in degrading linear RNA. You should see a significant decrease in linear RNA level while the circRNA level should not change much. If both the linear and circRNA levels change in the same direction after RNase R treatment, then either the RNase R may not be working well or the predicted circRNA is not a real circular RNA.

Mr lonoce...
Can I get your working experience..
Did u select Linear or circ GADPH as the reference control on space.
If the linear one..how did u calculate felt delta ct of it circular...
Then if results didn't differ before or after Rnase treatment then rnase has no significant effect ..no need for its use

Thanks Mr.panda for help but forgive me did u use circular GADPH as a control in rnase treated samples or what ..I didn't get the idea

Working on human Pvt1 cicular RNA I had the same result with untreated samples and samples subjected to Rnase R .

The level of GAPDH or any linear RNA will be very low after RNase R treatment. You can compare the Ct values of same circRNA or mRNA between RNase R and control treated sample to check their resistance to RNase R as described in the protocol. If you want to see the amount of linear RNA (e.g. mRNA X) left after RNase R digestion, you can use the counterpart circRNA (e.g. circRNA X) for normalisation using the delta delta Ct method.