FOR side := -1 TO +1 BY 2 DO
      IF side = +1 THEN tag :=  "apv" ELSE tag := "apf" END;
      SPPlot.Everything(
        func := UValue,
        tri := tri,
        outName := o.outName & "-val-" & tag,
        fMax := fMax,
        fStep := FLOAT(fMax/10.0d0, REAL),
        M := o.gridSize, N := o.gridSize,
        obs := obs,
        upp := HLR3.Point{c := LR4.T{0.0d0, 0.0d0, 0.0d0, 1.0d0}},
        dLight := LR3.T{0.0d0, 0.0d0, 1.0d0},
        eps := TRUE,
        verbose := TRUE
      );
      SPPlot.Everything(
        func := UError,
        tri := tri,
        outName := o.outName & "-err-" & tag,
        fMax := eMax,
        fStep := FLOAT(eMax/10.0d0, REAL),
        M := o.gridSize, N := o.gridSize,
        obs := obs,
        upp := HLR3.Point{c := LR4.T{0.0d0, 0.0d0, 0.0d0, 1.0d0}},
        dLight := LR3.T{0.0d0, 0.0d0, 1.0d0},
        eps := TRUE,
        verbose := TRUE
      );
      (* Reverse position of observer: *)
      FOR k := 1 TO 3 DO obs.c[k] := - obs.c[k] END;
    END


    
    eMax := FIRST(LONG);
    fMax := FIRST(LONG);
    FOR i := -10 TO +10 DO
      FOR j := -10 TO +10 DO 
        FOR k := -10 TO +10 DO
          IF i # 0 OR j # 0 OR k # 0 THEN
            WITH
              x = FLOAT(i, LONG),
              y = FLOAT(j, LONG),
              z = FLOAT(k, LONG),
              p = LR3.Dir(LR3.T{x, y, z}),
              fp = f.eval(p),
              up = u.eval(p),
              afp = ABS(fp),
              aep = ABS(up - fp)
            DO
              IF afp > fMax THEN fMax := afp END;
              IF aep > eMax THEN eMax := aep END;
            END;
          END;
        END;
      END;
    END;



      fMax: LONGREAL;        (* Nominal max absolute function value. *)
      fStep: REAL;           (* Value difference between successive level curves *)
      eMax: LONGREAL;        (* Nominal max absolute approx error. *)
      eStep: REAL;           (* Value difference between successive error level curves *)


        IF pp.keywordPresent("-fMax") THEN
          o.fMax := pp.getNextLongReal(0.0d0, LAST(LONGREAL))
        ELSE
          o.fMax := +1.0d0
        END;
        
        IF pp.keywordPresent("-fStep") THEN
          o.fStep := pp.getNextReal()
        ELSE
          o.fStep := 0.1
        END;
        
        IF pp.keywordPresent("-eMax") THEN
          o.eMax := pp.getNextLongReal(0.0d0, LAST(LONGREAL))
        ELSE
          o.eMax := +1.0d0
        END;
        
        IF pp.keywordPresent("-eStep") THEN
          o.eStep := pp.getNextReal()
        ELSE
          o.eStep := 0.1
        END;