Shipment showing different miles while calculating the base cost-regarding

Hi,            

I had an issue with shipment while calculating the base cost. Shipment Loaded Distance showing 327.2 miles but in financial tab it shows different distance(247.56 miles).

Could anyone tell me why this kind of issue occurs in OTM.

Below are some points for your reference,

1.) For distance calculation we have PC miller and it calculates the distance based on the postal code but we didnt change the postal code for past two months.

2.) In shipment, there is one check box called COST_FIXED. It was checked when the shipment was created. After deselecting the Cost Fixed check box and i perform the ReRate action, at that time it took the loaded distance 327.2 miles.