If a is average number of peaks more than 10 mm of uneveness per kilometre, b is average number peaks more than 6 mm for gauge variation per kilometre and c is average number of peaks more than 2 mm twist per metre, then composite current recording index (Ic), as recommended by Indian Northern Railways, is

• Ic = 10 - a - b - c/4
• Ic = 20 - a - b - c/4
• Ic = 30 - a - b - c/4
• Ic = 40 - a - b - c/4