Sales Order Total Weight

Hi All,

Can any one help me in this requirement like i want to get the Total Gross weight and volume of a Sales order how to get this

for that i use this like i have taken all the weights and volumes for that line items of a particular sales order and need to add those weights for that what to dooo??

and which is better to use like collect and Sum

and is there any way to do this requirement

Thanks

Surendra