Field reversed configurations with a racetrack shaped separatrix of variable length and constant radius rs are studied by assuming time-dependent uniform temperature and resistivity η. Only the most useful solutions, namely those with separated radial and time variables, are investigated. The decay times of all relevant quantities are related to those of the magnetic field, tB, the mass inventory, tM, and the length, tL. ηtB and ηtM are shown to be constant in time, tL is related to the rate of heat loss, tH. The configuration inside the separatrix is characterized by two parameters, 0 ≤ α < ∞ and 0 ≤ βs < 1, where α = tB/tM and βs is the value of beta on the separatrix. Global parameters such as the average beta and the fraction of trapped flux as well as the radial profiles of a number of quantities are shown graphically as functions of α and βs. It is pointed out that tB and tM can assume wide ranges of values for fixed η and rs. Therefore, the data of tB, tM and rs are necessary to assign a value of η to an experiment. Three conditions for maintaining an internal configuration characterized by (α, βs) throughout an experiment are proposed and evaluated numerically. These can be used for the prediction and control of an FRC. The external configuration is studied with a tentative model and the non-existence of a plasmavacuum interface is shown. For practical purposes, however, the depth of the external plasma layer can be defined and calculated as a function of α and βs. All parameters of the model can be determined for any experiment from the data of measurable global quantities, so that the inner configuration can be inferred. The resistivities assigned to current experiments range from one to ten times the classical value.