There are two basic ways to use a straight key, and key design usually reflects one of the two "styles."
In the American style, you send with your forearm resting on the table. Typically the knob is a flat disk, located an inch or so above the surface of the operating table, and the key is placed toward the back of the table.
In the European style, the key is placed at the front or near edge of the table, and your forearm is unsupported. Ideally your forearm is parallel to the floor. European style keys typically have a straight lever and a round knob located more than an inch above the table surface.