The main goal of this practice mode is to learn not to add too much extension during the backswing and then remove the extension during the downswing.
Extension is a positive value, also called cupping of the wrist. More extension opens the club face, steepens the shaft.
Flexion is a negative value, also called the bowing of the wrist. More flexion closes the club face, shallows the shaft.
The three data points in the app represent extension and flexion data at address, top and impact.
Address: Weaker grips usually have less extension, around 10-20 degrees at address, stronger grips have more extension, 30-40 degrees.
Top: Stronger grips are more extended at the top, often 20-30 degrees. Weaker grips are less extended at the top or even flexed.
Impact: Stronger grips are a bit more extended at impact, around 0-10 degrees, weaker grips are more flexed at impact.
The more extension you add, the more you open your clubface. If the clubface is too open it is difficult to consistently close the clubface during the downswing.
The more extension is removed from the address, the more the wrist gets flexed (bowed) and the club gets delofted, producing more shaft lean.