About 15 years ago, when I was having regular doctors visits for what turned out to be a cyst on my penis following an earlier circumcision, I was measured.
I never found out what the survey was for, but after one of my regular exams, I was asked if I'd mind taking part in a survey on body size. I agreed. By now I was already redressed, so I left the doctors room and went off with the nurse.
We went into another room in the surgery and she asked if it was okay for another nurse to come in, again I agreed. I'd been examined here quite a lot, so most of the nurses had already seen my bits anyway, but I wasn't sure what this was all about.
The second nurse came in and they said they wanted to measure all of my body as part of a survey into modern human averages. The first nurse then said if I didn't mind they'd like me naked. As I said, they'd already seen me when I'd been examined previously, so I stripped off.
The first nurse took all of the measurements and the second wrote down the results. Height, waist, arm length, leg length... Everything was measured and recorded. After everything was done, she then measured the length and girth of my flaccid penis, then my balls. I was then made erect and measured again.
I dressed and left, never knowing what I just contributed to.
The next visit I made the doctor did thank me again for taking part