re obtained from observations and they have little rooms for adjustment. The general principle was that values of <span class="nowrap">r<sub>1</sub></span> and <span class="nowrap">r<sub>2</sub></span> cannot deviate from observations by more than 0.01 days. If it is impossible to find <span class="nowrap">R<sub>1</sub></span> and <span class="nowrap">R<sub>2</sub></span> within the acceptable range, another set of U, T and A has to be chosen so that <span class="nowrap">U/A</span> and <span class="nowrap">