Interpolating from several standard curves on one Prism table.

Interpolating can go in both directions. Calculating Y from X is no problem. Calculating X from Y is more useful, but presents some issues when you have multiple data sets. Prism can interpolate several data sets from one table, but note the following:

• Prism has to figure out which values are unknowns. It uses this rule: X(or Y) values are considered as unpaired (and are used for calculation of unknowns) when they are lower in the table than all XY pairs in the data table. It is not enough that the upaired Y values (from which you want Prism to interpolate X) is lower on the table than the paired XY values for that particular data set. They must be on lower rows in the table than all the paired XY values of all data sets in the table. 
• Prism 5.01 and 5.0b offer an option in the Output tab of nonlinear regression that let you choose where the interpolated X values should go (into the X column staggered, or onto Y columns). If you have replicates and have unknowns in more than one data set, choose the option to show the unknowns in Y columns. 
• Prism 2 and 3 can only analyze one standard curve at a time (computing X from unknown Y values) . If you enter several data sets on one table, analyze that table several times. After the first analysis is complete, duplicate the results sheet. Then click "Change.. Data analyzed". Select only one data set (column) to analyze. Repeat for each data set on your table.