in example 1 but the time during which the insulated conductor passes the tube 17 is about 0 5 minutes the degree of cross linking in the polyethylene can be established and controlled and adjusted in the manner indicated in example 1 in an alternative method of determining the degree of cross linking in the device according to fig1 a preformed product is used in the form of a strip of polyethylene containing a cross linking indicator the strip is fed in along the conductor when entering the extrusion machine as described in example 1 the strip has the same composition as the compound which is to form the insulation however possibly without peroxide and antioxidant and apart from the fact that the compound forming the insulation does not contain any cross linking indicator manufacture of the insulated conductor takes place in the same way as has been described previously to establish the degree of cross linking in the finished insulated conductor a cross section thereof is cut off shown in fig8 where the strip with the cross linking indicator is designated 23 the color of the cross linking indicator is then compared with a calibrated scale and any measures required for controlling the cross linking reaction in the conductor insulation are thereafter taken an insulated cable conductor is manufactured in the manner indicated in example 5 with the difference that instead of the cross linking indicator mentioned there there is used as cross linking indicator the same amount of the previously mentioned compound with the.