diff --git a/histogram_internal.h b/histogram_internal.h
new file mode 100644
index 0000000..f4cc286
--- /dev/null
+++ b/histogram_internal.h
@@ -0,0 +1,4 @@
+#pragma once
+#include <vector>
+
+void find_minmax(const  std::vector<double>& numbers, double& min, double& max);
\ No newline at end of file
diff --git a/lab1.vcxproj b/lab1.vcxproj
index 8f1ff1c..ce5422b 100644
--- a/lab1.vcxproj
+++ b/lab1.vcxproj
@@ -133,6 +133,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="histogram.h" />
+    <ClInclude Include="histogram_internal.h" />
     <ClInclude Include="text.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
diff --git a/lab1.vcxproj.filters b/lab1.vcxproj.filters
index a753087..7e1d14f 100644
--- a/lab1.vcxproj.filters
+++ b/lab1.vcxproj.filters
@@ -32,5 +32,8 @@
     <ClInclude Include="text.h">
       <Filter>Исходные файлы</Filter>
     </ClInclude>
+    <ClInclude Include="histogram_internal.h">
+      <Filter>Исходные файлы</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>
\ No newline at end of file