Probit and logit are equation-intensive and usually done on a computer. Moving average can be done with calculator, but requires log conc.
Graphic interpolation is appropriate only in the absence of calculator or computer.
The resulting curve is an estimate of the central portion of the toxicity distribution. Calculate the mean of the plotted distribution. This is the relative frequency for that interval. B. Calculate the average of the corresponding xi values. C. Multiply values from A. and B. above, and total those products.