With the help of the ǀΔTǀ = 1/2 rule the three nonleptonic sigma decay modes are described by four complex amplitudes with phases given by time reversal invariance. The four magnitudes are explicitly expressed as functions of four measurable quantities, the three decay rates and the parameter α-. The remaining decay parameters are then written in terms of four measurable quantities. These relations take account of the scattering phase shifts, the differences in phase space for the three decays, and possible inequalities in the decay rates. The relations are used (a) to check the validity of the ǀΔTǀ = 1/2 rule and time reversal invariance, (b) to calculate parameters of the decay that have not yet been measured and (c) to discuss the importance of measuring βi.