Every column you give the recommender must be linked to a known clothing measurement so the system knows what it means. Two columns cannot share a link. Each link has three parts, and all three matter.
1. Which measurement it is
Pick the measurement that matches what your size chart column actually contains.
2. Whether it measures the garment or the body
A garment measurement gets ease added to the shopper's body before comparing. A body measurement is compared directly with no ease.
Choosing body when your size chart lists garment measurements makes every size read tighter than it is.
3. Full circumference or half
Choose half when your size chart lists a flat, laid-out measurement — the width of the garment lying on a table. Choose full when it lists a measurement taken all the way round.
Getting this backward makes the garment read at half or double its real size. This is one of the most common causes of badly wrong recommendations.
Which measurements actually change the result
Not every linked measurement affects the outcome. These always count:
Chest
Waist
Hip
Shoulder
Thigh
Bicep
Collar
Shirt length
Height
Sleeve opening counts on shirts, blazers and jackets. Inseam, leg opening and bottom length count on bottoms.
Measurements that are offered but never used
These can be linked without any error, but they will not change the recommended size:
Sleeve length
Hem
Under bust
Front rise
Back rise
If you linked sleeve length expecting it to affect results, that is why nothing changed.