Original Duartion Increase and Comapre with BL Original Duration

Hi,

I need to increase the original duration  for some activites due to additional work and see how the Project key dates affected.

I have the original Program with original Program base line assigned. No progress updated. so  actual duration is zero.

Then I increase the original duration  for required activities and run the schedule ( Data Date Project start date).  The key dates correctly shifted.

I incude the colums Original duration, BL1 Duration and Variance BL1 Duration for comparison. But i notice the BL1 base line duration  reduced. and hence the BL1 Variance also increased.

Some time the BL1 Original duration does not decrease and shows correctly. Most of the time it get reduced.

Please advice the correct method to comapre the  Baseline original duration and current increase original duration and the varianace original duration.

Regards

Kasi