While doing the examine plot subdialog I noticed two problems with the spreadlevel plots.

a) The syntax parser only accepts integer value for the t value. This does not allow to compute square root (0.5) or reciprocal square root (-0.5) scalings of the data although this seems to be a reasonable thing to do.

see: http://www.unige.ch/ses/sococ/cl/spss/eda/spreadlevelplot.html

b) I think there is a difference in the understanding between SPSS and PSPP with respect to the spreadlevel plot, but I am not sure. Here is the SPSS description:

SPREADLEVEL(n). Spread-versus-level plot with the Test of Homogeneity of Variance table. If the keyword appears alone, the natural logs of the interquartile ranges are plotted against the natural logs of the medians for all cells. If a power for transforming the data (n) is given, the IQR and median of the transformed data are plotted. If 0 is specified for n, a natural log transformation of the data is done.

see: https://www.ibm.com/support/knowledgecenter/SSLVMB_sub/statistics_reference_project_ddita/spss/base/syn_examine_plot.html

The gui has a selection "Power Estimation" and that refers to the mode: "If the keyword appears alone, the natural logs of the interquartile ranges are plotted against the natural logs of the medians for all cells."

Is "Power Estimation" different from SPREADLEVEL(0) ? In the PSPP docs this is the same. But aren't the natural logs of the interquartile ranges different from interquartile ranges of transformed data?