Alber Percival was issued a British patent dated February 11, 1926 to cover his PerWhit putter.  The blade is convex, top to bottom.  To Percival, the curved blade allowed for more consistent contact with the ball no matter if the player varied the position of the shaft from one stoke to the next.  The curve extending all the way down to the sole would tend to prevent the blade from dragging or clinging to the turf on either the backswing or follow through.

This PerWhit putter shows very little use. The shaft is original. The leather-wrap grip is a replacement but matches up well to the club, drawing no undue attention.

TCA2 V1: p296-297