Four pad self-calibrating electronic lapping guide

A method for making a magnetic recording head, comprising the steps of:

• lapping along a lapping plane of a slider bar, the slider bar including a first differential electronic lapping guide (ELG) disposed in a first layer and a second differential ELG disposed in a second layer different from the first layer, the first differential ELG having a first resistive element and a second resistive element between which is disposed a first common electrical lead, the second differential ELG having a third resistive element and a fourth resistive element between which is disposed a second common electrical lead, the first and second differential ELGs sharing a common ground and a common current injection source distinct from the first common electrical lead and the second common electrical lead, the lapping removing a portion of the slider bar;
• measuring, while the lapping occurs, a first voltage V1 between the common current injection source and the common ground, a second voltage V2 between the first common electrical lead and the common ground, and a third voltage V3 between the second common electrical lead and the common ground;
• and
• determining whether to change either a rate of the lapping or an angle of the slider bar based upon the measured first, second and third voltages.

A non-transitory machine readable medium carrying one or more sequences of instructions for making a magnetic recording head, wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to perform the steps of:

• lapping along a lapping plane of a slider bar, the slider bar including a first differential electronic lapping guide (ELG) disposed in a first layer, and a second differential ELG disposed in a second layer different from the first layer, the first differential ELG having a first resistive element and a second resistive element between which is disposed a first common electrical lead, the second differential ELG having a third resistive element and a fourth resistive element between which is disposed a second common electrical lead, the first and second differential ELGs sharing a common ground and a common current injection source;
• measuring, while the lapping occurs, a first voltage V1 between the common current injection source and the common ground, a second voltage V2 between the first common electrical lead and the common ground, and a third voltage V3 between the second common electrical lead and the common ground;
• and
• determining whether to change either a rate of the lapping or an angle of the slider bar based upon the measured first, second and third voltages.