diff --git a/extensions/fablabchemnitz/hatch_fill/hatch_fill.inx b/extensions/fablabchemnitz/hatch_fill/hatch_fill.inx
index 174e969e..a1683d50 100644
--- a/extensions/fablabchemnitz/hatch_fill/hatch_fill.inx
+++ b/extensions/fablabchemnitz/hatch_fill/hatch_fill.inx
@@ -7,13 +7,13 @@
             <label xml:space="preserve">This extension fills each closed figure in your drawing with a path consisting of back and forth drawn "hatch" lines. If any objects are selected, then only those selected objects will be filled. 
 
 Hatched figures will be grouped with their fills.</label>
-            <param name="hatchSpacing" type="float" min="0.1" max="1000" gui-text="Hatch spacing">3.0</param>
+            <param name="hatchSpacing" type="float" min="0.001" max="1000" precision="3" gui-text="Hatch spacing">3.0</param>
             <param name="hatchAngle" type="float" min="-360" max="360" gui-text="Hatch angle (degrees)">45</param>
             <param name="crossHatch" type="bool" gui-text="Crosshatch?">false</param>
             <param name="reducePenLifts" type="bool" gui-text="Connect nearby ends?">true</param>
-            <param name="hatchScope" type="float" min="0.1" max="10.0" gui-text="Range of end connections (default: 3)">3.0</param>
+            <param name="hatchScope" type="float" min="0.001" max="10.0" precision="3" gui-text="Range of end connections (default: 3)">3.0</param>
             <param name="holdBackHatchFromEdges" type="bool" gui-text="Inset fill from edges?">true</param>
-            <param name="holdBackSteps" type="float" min="0.1" max="10.0" gui-text="Inset distance (default: 1)">1.0</param>
+            <param name="holdBackSteps" type="float" min="0.001" max="10.0" precision="3" gui-text="Inset distance (default: 1)">1.0</param>
             <param name="tolerance" type="float" min="0.1" max="100" gui-text="Tolerance (default: 3.0)">3.0</param>
             <label xml:space="preserve">(v0.9.0b, July, 2020)</label>
         </page>
diff --git a/extensions/fablabchemnitz/slic3r_stl_input/slic3r_stl_input.py b/extensions/fablabchemnitz/slic3r_stl_input/slic3r_stl_input.py
index 3ca2adf8..4042ce36 100644
--- a/extensions/fablabchemnitz/slic3r_stl_input/slic3r_stl_input.py
+++ b/extensions/fablabchemnitz/slic3r_stl_input/slic3r_stl_input.py
@@ -112,6 +112,10 @@ class SlicerSTLInput(inkex.EffectExtension):
 
     def effect(self):             
         args = self.options
+     
+        if not os.path.exists(args.slic3r_cmd):
+            inkex.utils.debug("Slic3r not found. Please define a correct location.")
+            exit(1)
         
         if args.min_fill_opacity > args.max_fill_opacity:
             inkex.utils.debug("Min fill opacity may not be larger than max fill opacity. Adjust and try again!")