Well how do we know that any scale at all is right?
My lab has weights that get calibrated against a NIST standard annually. We use those weights to perform daily quality control that our scale is accurate (to +/- 0.01g). If the quality control fails then we recalibrate the scale.
In the US, it is an Individual Donor Assessment and applies to everyone. Everyone gets the same question tree, regardless of sexual orientation. If you have had a new partner in the last 3 months or have multiple partners that doesn’t defer you, it sends you to the next tier of question: have you engaged in anal sex. Yes to anal with a new partner or multiple partners is the deferral. If you haven’t had a new partner or multiple partners in the last 3 months, you will not be asked about anal sex. Canada went live with their individual donor assessment a year before the US and has noted a slight drop in donations in straight donors because they are now being deferred for high risk activity when they were previously missed.
Prep is listed under a medication deferral. First responders that take prep for protection from workplace exposure are deferred as well.
(I’m a blood banker)