A pressure gauge where a main wheel (11) is rotated to raise and lower the upper one of two horizontal feed rollers of a laminating machine so that the pressure applied by the rollers is the same in successive operations. A mark on an indexing wheel (14), which rotates with the main wheel (11), is brought into alignment with a mark on the casing (10) of the machine. The outer ring (14) of the indexing wheel is manually rotatable relative to its inner ring (13), but is held in frictional contact with the main wheel (11) by compression springs (17).