Using coordinated TRACE and EIT observations, we discussed which pair of coronal abundances and ionization equilibrium assumption will give the least difference of temperature and emission maps. It is found that the combination meyer_coronal.abund and shull.ioneq gives the smallest difference between TRACE and EIT observations among the 42 pairs of combination, while the difference between each pair is not much. The difference between temperature or emission maps from coordinated TRACE and EIT observations may be regarded as an estimation of the accuracy of the temperature or emission maps using this kind of method. Under this assumption, the error for temperature diagnosis is estimated at Δ(log10T) = 0.01 and the error for emission diagnosis is estimated at Δ(log10EM) = 0.08 at largest.