Line charts show counts only

Greetings ... trying to implement a weight tracking chart.

Have followed your example in my vault.

All I see is a straight line plotted, since each date has 1 value of @weight.

How to I change from occurrences to values in a tracker line chart?   

I've read the page on "constValue" but I can't understand how to implement it.

Thanks for any help with this amazing plug-in!