diff --git a/rtdata/languages/default b/rtdata/languages/default
index 3911dc12a..4ecc85b70 100644
--- a/rtdata/languages/default
+++ b/rtdata/languages/default
@@ -1982,7 +1982,7 @@ TP_LOCALLAB_CURVEEDITOR_CC_TOOLTIP;If curves at the top, mask is completely blac
 TP_LOCALLAB_CURVEMETHOD_TOOLTIP;'Normal', the curve L=f(L) has the same algorithm than slider lightness.\n'Super' the curve L=f(L) has an new improved algorithm, which can leeds in some cases to artifacts.
 TP_LOCALLAB_EXCLUF;Excluding
 TP_LOCALLAB_EXCLUF_TOOLTIP;Can be used to exclude this part of datas - move Scope to extend color.\n You can apply all settings to this RT-spot.
-TP_LOCALLAB_LABGRID_VALUES;HL: a=%1 b=%2\nS: a=%3 b=%4
+TP_LOCALLAB_LABGRID_VALUES;a(L)=%1 b(L)=%2\na(a)=%3 b(a)=%4
 TP_LOCALLAB_LABGRID;Color correction grid
 TP_LOCALLAB_SENSIDEN;Scope
 TP_LOCALLAB_SENSIEXCLU;Scope
diff --git a/rtengine/iplocallab.cc b/rtengine/iplocallab.cc
index b7cbb9dca..9650655f1 100644
--- a/rtengine/iplocallab.cc
+++ b/rtengine/iplocallab.cc
@@ -7952,11 +7952,11 @@ void ImProcFunctions::Lab_Local(int call, int sp, float** shbuffer, LabImage * o
 
 
 //local color and light
-        const float factor = ColorToningParams::LABGRID_CORR_MAX * 3.f;
-        const float scaling = ColorToningParams::LABGRID_CORR_SCALE;
-        float a_scale = 2.f * (lp.highA - lp.lowA) / factor / scaling;
+        const float factor = LocallabParams::LABGRIDL_CORR_MAX * 3.28f;
+        const float scaling = LocallabParams::LABGRIDL_CORR_SCALE;
+        float a_scale = (lp.highA - lp.lowA) / factor / scaling;
         float a_base = lp.lowA / scaling;
-        float b_scale = 2.f * (lp.highB - lp.lowB) / factor / scaling;
+        float b_scale = (lp.highB - lp.lowB) / factor / scaling;
         float b_base = lp.lowB / scaling;
         bool ctoning = (a_scale != 0.f || b_scale != 0.f || a_base != 0.f || b_base != 0.f);
         if (!lp.inv  && (lp.chro != 0 || lp.ligh != 0.f || lp.cont != 0 || ctoning || lp.qualcurvemet != 0 || lp.showmaskcolmet == 2 || lp.enaColorMask || lp.showmaskcolmet == 3  || lp.showmaskcolmet == 4) && lp.colorena) { // || lllocalcurve)) { //interior ellipse renforced lightness and chroma  //locallutili
@@ -8372,7 +8372,6 @@ void ImProcFunctions::Lab_Local(int call, int sp, float** shbuffer, LabImage * o
                     LabImage *bufcolcalc = nullptr;
                     bufcolcalc = new LabImage(bfw, bfh);
 
-                    //printf("a_s=%f a_b=%f b_s=%f b_b=%f \n", a_scale, a_base, b_scale, b_base);
 
 #ifdef _OPENMP
                     #pragma omp parallel for schedule(dynamic,16)
diff --git a/rtengine/procparams.cc b/rtengine/procparams.cc
index f0ebaba66..362b5cc19 100644
--- a/rtengine/procparams.cc
+++ b/rtengine/procparams.cc
@@ -2366,6 +2366,7 @@ LocallabParams::LocallabSpot::LocallabSpot() :
     labgridBLow(0.0),
     labgridAHigh(0.0),
     labgridBHigh(0.0),
+
     strengthgrid(20),
     sensi(15),
     structcol(0),
@@ -2646,6 +2647,9 @@ bool LocallabParams::LocallabSpot::operator !=(const LocallabSpot& other) const
     return !(*this == other);
 }
 
+const double LocallabParams::LABGRIDL_CORR_MAX = 10000.f;
+const double LocallabParams::LABGRIDL_CORR_SCALE = 3.28f;
+
 LocallabParams::LocallabParams() :
     enabled(false),
     nbspot(0),
diff --git a/rtengine/procparams.h b/rtengine/procparams.h
index c43259a10..2507253bb 100644
--- a/rtengine/procparams.h
+++ b/rtengine/procparams.h
@@ -1090,6 +1090,8 @@ struct LocallabParams {
     };
 
     bool enabled;
+    static const double LABGRIDL_CORR_MAX;
+    static const double LABGRIDL_CORR_SCALE;
     int nbspot;
     int selspot;
     std::vector<LocallabSpot> spots;
diff --git a/rtgui/locallab.cc b/rtgui/locallab.cc
index ed5a42400..7add8f807 100644
--- a/rtgui/locallab.cc
+++ b/rtgui/locallab.cc
@@ -1509,10 +1509,10 @@ void Locallab::write(ProcParams* pp, ParamsEdited* pedited)
                     pp->locallab.spots.at(pp->locallab.selspot).chroma = chroma->getIntValue();
                     labgrid->getParams(pp->locallab.spots.at(pp->locallab.selspot).labgridALow, pp->locallab.spots.at(pp->locallab.selspot).labgridBLow, pp->locallab.spots.at(pp->locallab.selspot).labgridAHigh, pp->locallab.spots.at(pp->locallab.selspot).labgridBHigh);
                     pp->locallab.spots.at(pp->locallab.selspot).strengthgrid = strengthgrid->getIntValue();
-                    pp->locallab.spots.at(pp->locallab.selspot).labgridALow *= ColorToningParams::LABGRID_CORR_MAX;
-                    pp->locallab.spots.at(pp->locallab.selspot).labgridAHigh *= ColorToningParams::LABGRID_CORR_MAX;
-                    pp->locallab.spots.at(pp->locallab.selspot).labgridBLow *= ColorToningParams::LABGRID_CORR_MAX;
-                    pp->locallab.spots.at(pp->locallab.selspot).labgridBHigh *= ColorToningParams::LABGRID_CORR_MAX;
+                    pp->locallab.spots.at(pp->locallab.selspot).labgridALow *= LocallabParams::LABGRIDL_CORR_MAX;
+                    pp->locallab.spots.at(pp->locallab.selspot).labgridAHigh *= LocallabParams::LABGRIDL_CORR_MAX;
+                    pp->locallab.spots.at(pp->locallab.selspot).labgridBLow *= LocallabParams::LABGRIDL_CORR_MAX;
+                    pp->locallab.spots.at(pp->locallab.selspot).labgridBHigh *= LocallabParams::LABGRIDL_CORR_MAX;
                     pp->locallab.spots.at(pp->locallab.selspot).sensi = sensi->getIntValue();
                     pp->locallab.spots.at(pp->locallab.selspot).structcol = structcol->getIntValue();
                     pp->locallab.spots.at(pp->locallab.selspot).blurcolde = blurcolde->getIntValue();
@@ -2591,7 +2591,7 @@ void Locallab::setDefaults(const ProcParams * defParams, const ParamsEdited * pe
     lightness->setDefault((double)defSpot->lightness);
     contrast->setDefault((double)defSpot->contrast);
     chroma->setDefault((double)defSpot->chroma);
-    labgrid->setDefault(defSpot->labgridALow / ColorToningParams::LABGRID_CORR_MAX, defSpot->labgridBLow / ColorToningParams::LABGRID_CORR_MAX, defSpot->labgridAHigh / ColorToningParams::LABGRID_CORR_MAX, defSpot->labgridBHigh / ColorToningParams::LABGRID_CORR_MAX);
+    labgrid->setDefault(defSpot->labgridALow / LocallabParams::LABGRIDL_CORR_MAX, defSpot->labgridBLow / LocallabParams::LABGRIDL_CORR_MAX, defSpot->labgridAHigh / LocallabParams::LABGRIDL_CORR_MAX, defSpot->labgridBHigh / LocallabParams::LABGRIDL_CORR_MAX);
     sensi->setDefault((double)defSpot->sensi);
     structcol->setDefault((double)defSpot->structcol);
     blurcolde->setDefault((double)defSpot->blurcolde);
@@ -3708,7 +3708,7 @@ void Locallab::updateLocallabGUI(const rtengine::procparams::ProcParams* pp, con
         lightness->setValue(pp->locallab.spots.at(index).lightness);
         contrast->setValue(pp->locallab.spots.at(index).contrast);
         chroma->setValue(pp->locallab.spots.at(index).chroma);
-        labgrid->setParams(pp->locallab.spots.at(index).labgridALow / ColorToningParams::LABGRID_CORR_MAX, pp->locallab.spots.at(index).labgridBLow / ColorToningParams::LABGRID_CORR_MAX, pp->locallab.spots.at(index).labgridAHigh / ColorToningParams::LABGRID_CORR_MAX, pp->locallab.spots.at(index).labgridBHigh / ColorToningParams::LABGRID_CORR_MAX, false);
+        labgrid->setParams(pp->locallab.spots.at(index).labgridALow / LocallabParams::LABGRIDL_CORR_MAX, pp->locallab.spots.at(index).labgridBLow / LocallabParams::LABGRIDL_CORR_MAX, pp->locallab.spots.at(index).labgridAHigh / LocallabParams::LABGRIDL_CORR_MAX, pp->locallab.spots.at(index).labgridBHigh / LocallabParams::LABGRIDL_CORR_MAX, false);
         strengthgrid->setValue(pp->locallab.spots.at(index).strengthgrid);
         sensi->setValue(pp->locallab.spots.at(index).sensi);
         structcol->setValue(pp->locallab.spots.at(index).structcol);