What is the reason for the change from 2 to 3 guide dots (GD) in the left bottom corner?

What is the reason for the change from 2 to 3 guide dots (GD) in the left bottom corner?
The 2 GDs date back to the time when customers also used other scanners. Now all customers use scanners with barcode readers – thus the orientation is given by the barcode (If customers put the slide into the reader the other way around the barcode will not be scanned).
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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.