scale down histogram button movement by 10, was very sensitive

source/blender/editors/interface/interface_handlers.c

@@ -3868,9 +3868,9 @@ static int ui_numedit_but_HISTOGRAM(uiBut *but, uiHandleButtonData *data, int mx
 		hist->height = (but->y2 - but->y1) + (data->dragstarty - my);
 	}
 	else {
-		/* scale histogram values */
+		/* scale histogram values (dy / 10 for better control) */
 		const float yfac = minf(powf(hist->ymax, 2.0f), 1.0f) * 0.5f;
-		hist->ymax += dy * yfac;
+		hist->ymax += (dy * 0.1f) * yfac;
 	
 		/* 0.1 allows us to see HDR colors up to 10 */
 		CLAMP(hist->ymax, 0.1f, 100.f);