To indicate an angled surface and make that surface parallel to a surface plate, a machinist uses:

The sine plate is specifically designed for setting and measuring angles, making it highly effective for aligning angled surfaces with precision. By using a sine plate, a machinist can create a known angle by adjusting the height of one side, which allows for a smooth and controlled process of making the surface parallel to a surface plate. The ability of the sine plate to establish angular relationships accurately makes it a valuable tool in machining and measurement tasks where accuracy is critical.

V-blocks are generally utilized for holding cylindrical workpieces securely during machining or measurements but do not provide the capability to set angles. Gage blocks are used for achieving precise lengths or calibrating measurements but are not designed for angle adjustments. Alignment bars serve various purposes in aligning components but lack the specific functionality of addressing angled surfaces. Hence, the sine plate stands out as the appropriate choice when the objective is to indicate an angled surface and ensure its parallelism to a surface plate.