aintlifegrand,

There are two possible intentions of yours that are difficult to reveal:

- To insert a new characteristic into the family of the existing ones, with

a new value of parameter (size, design parameter, power etc.) that determines

each of your series. This could(!) be resolved, indeed, by trendlining the

other series, at least in the decisive part of the characteristics, most

probably by a three-parameter regression. These three parameters should be

each further fitted by the next (linear, i.e. two-parameter) regressions on

the discussed parameter. Fortunately, at least one of these relationships

should be almost constant (similar shapes opf curves). By a simple

mathematical treatment you should obtain a general (six-parameter)equation

for a characteristic line where you will substitute independent variable and

a new parameter.

- To draw efficiency lines. If you should come out only from tabulated data

including efficiencies, you could be lucky enough to find out the proper

number of point co-ordinates valid for each selected value of efficiency. The

simple task would be only to gather them properly to a chart series range. If

the data would be too scarce, than you would have ahead a more complicated

work with interpolations.

Regards