position question, cylinder vs circle, what do you do?

Question

I am currently using PCDMIS 2019 and have a couple questions for the experts. 
 1.) When measuring position using xact, let's say back to datums A, B, C to keep things simple, do you use a cylinder or a circle? 
 2.) When do you use a cylinder? do you only use a cylinder when perpendicularity is called out? when do you use a circle? 
 3.) When using a cylinder for position, what does "FIT TO DATUMS=ON" mean, and what does "USE AXIS=WORST" mean? In the report window next to the feature name, what does (START PT) mean?

utku.yucekutlu · Answer

You must try to use cylinder where it is possible. Use circle only if lenght is not long enough. 
 When using Xact (or GeoTol in newer versions), and with selection of GD&T Standards (ISO or ASME), calculation of a cylinder's position depends on your measurement circles within cylinder. 
 If you are using ASME, software looks at your start and end points and gives you the worst one. However, do not confuse this as it is not your measurements' start and end but cylinders' start or end points. So it is better to measure the cylinder as long as possible. 
 If you are using ISO, the worst level is reported. 
 For ASME: 
 
 For ISO:

Hope it helps.