The chart indicates that both grey lines are "1.55 x smoothed peak book value", and the yellow line is "WMA16 * 1.55". Is the latter 1.55 * average book values over the most recent 16 quarters?

Jim just explained WMA and specifically WMA16.

Regarding my chart:
- The upper grey line is 1.55 x PeakBV (Peak = Highest BV up to that date)
- The lower grey line is 1.15 x PeakBV (Peak = Highest BV up to that date)
- The yellow line is 1.55 x WMA16

P.S.: In line with Jim´s former posts WMA16 actually for smoothing purposes is calculated a bit more complex: Not simply WMA16 of PeakBV, but "WMA16 of the greater of BV and 90% x PeakBV".

P.P.S.: Don't let yourself be confused by 2x the value "1.55" being used, for the upper grey and for the yellow line, which might give the wrong impression that value must be identical for both lines. It´s purely accidental, just seems to give the best fit, for the channel in which BRK usually trades, and for that WMA line in it. If e.g. I would have used 1.10 and 1.60 for the grey lines the channel simply would have been a little wider, with the yellow 1.55 x WMA16 line still in the middle of that wider channel.