A particular kind of quintessence is considered , with equation of motion p _ { Q } / \rho _ { Q } = -1 , corresponding to a cosmological term with time-dependence \Lambda ( t ) = \Lambda ( t _ { 0 } ) ( R ( t _ { 0 } ) / R ( t ) ) ^ { P } which we examine initially for 0 \leq P < 3 .
Energy conservation is imposed , as is consistency with big-bang nucleosynthesis , and the range of allowed P is thereby much restricted to 0 \leq P < 0.2 .
The position of the first Doppler peak is computed analytically and the result combined with analysis of high-Z supernovae to find how values of \Omega _ { m } and \Omega _ { \Lambda } depend on P .
Some comparison is made to the CMBFAST public code .