Double keying and "requiring a duplicate entry"

Does anyone have any suggestions for how to require a replicate value be entered? As an example, we want to take 2 weight measurements and somehow enforce that the user has entered the second value. Other than setting up a validation that pops up after the first entry and goes away once the second value is added - does anyone have any suggestions? This is for a series of anthropometric measurements that typically require 2-3 values for each measurement.

Thanks,

-david p-

Close the rest of the interview until the second value is entered.

See also here:
https://support.mysurvey.solutions/questionnaire-designer/techniques/mandatory-required-questions/