An isoconversional state diagram (ISD) method is a graphical representation of the commonly used model free kinetics (MFK) method. An ISD state curve describes the relationship between 1/T and lnβ at a certain conversion degree, where T is the temperature and β is the heating rate. The ISD tangent rule describes the pattern of intersection of two tangents to two adjacent state curves at given points having the same temperature, which can be used for the correction of random error in the experimental thermal analysis data. The comparison of kinetic predictions between the ISD and MFK methods shows that the corrective effect is evident and the prediction quality can be improved in the predictable heating rate and temperature ranges. Furthermore, the proposed implicit method simplifies the ISD construction procedure compared to the previous explicit method.