3 files changed, 7 insertions, 3 deletions
diff --git a/lib/axlsx/drawing/num_data.rb b/lib/axlsx/drawing/num_data.rb
index 802a0216..ee6b145e 100644
--- a/lib/axlsx/drawing/num_data.rb
+++ b/lib/axlsx/drawing/num_data.rb
@@ -25,8 +25,8 @@ module Axlsx
     def data=(values=[])
       @tag_name = values.first.is_a?(Cell) ? :numCache : :numLit
       values.each do |value|
-        v = value.is_a?(Cell) ? value.value : value
-        @pt << NumVal.new(:v => v)
+        value = value.is_formula? ? 0 : value.value if value.is_a?(Cell)
+        @pt << NumVal.new(:v => value)
       end
     end
 
diff --git a/lib/axlsx/drawing/num_val.rb b/lib/axlsx/drawing/num_val.rb
index 35dbdb83..ed655732 100644
--- a/lib/axlsx/drawing/num_val.rb
+++ b/lib/axlsx/drawing/num_val.rb
@@ -26,7 +26,7 @@ module Axlsx
     # serialize the object
     def to_xml_string(idx, str = "")
       Axlsx::validate_unsigned_int(idx)
-      str << '<c:pt idx="' << idx.to_s << '" formatCode="' << format_code << '"><c:v>' << v.to_s.to_i.to_s << '</c:v></c:pt>'
+      str << '<c:pt idx="' << idx.to_s << '" formatCode="' << format_code << '"><c:v>' << v.to_s << '</c:v></c:pt>'
     end
   end
 end
diff --git a/lib/axlsx/workbook/worksheet/cell.rb b/lib/axlsx/workbook/worksheet/cell.rb
index 745809f9..e3e153e0 100644
--- a/lib/axlsx/workbook/worksheet/cell.rb
+++ b/lib/axlsx/workbook/worksheet/cell.rb
@@ -317,6 +317,10 @@ module Axlsx
       str << '</c>'
     end
 
+    def is_formula?
+      @type == :string && @value.start_with('=')
+    end
+
     private
 
     # Utility method for setting inline style attributes