Portfolio duration - notional or mkt value?

Quick thing: in volume 3, they use notional (usually equal for each component) to get the weighted average duration. (for example, practice problem number 4) But in volume 4, page 12, they use market value. What should we use to get portfolio duration? I would say market value (so their solution to practice problem number 4 would be wrong), but not 100% sure… thx

duration is the weighted average of the present value of the remaining cash flows. so by definition the market value is what you would implicitly use.