What changes if I add a diversifier?
Start from US equities alone, then move one other asset in. Over the exact period the two actually share, see what got calmer, what got shallower, and what it cost.
Your comparison
The base portfolio is 100% US equities. Whatever you add is taken out of it, so both portfolios always describe the same whole.
Changing the asset changes the period: the comparison only uses the history the two actually share, so it can be decades or a few years.
The dataset publishes the weight it accepts; the control opens when it answers.
Computing on the published dataset…