diff --git a/svg.cpp b/svg.cpp
index 7b1ccd0..2fcfa13 100644
--- a/svg.cpp
+++ b/svg.cpp
@@ -5,6 +5,14 @@
 
 using namespace std;
 
+bool
+check_width(double width) {
+    if (width >= 3 && width <= 30)
+        return true;
+    else
+        return false;
+}
+
 void
 svg_text(double left, double baseline, string text) {
     cout << "<text x='" << left
@@ -47,8 +55,16 @@ show_histogram_svg(const vector<size_t>& bins) {
     const auto TEXT_BASELINE = 20;
     const auto TEXT_WIDTH = 50;
     const auto BIN_HEIGHT = 30;
-    const auto BLOCK_WIDTH = 10;
+    double BLOCK_WIDTH = 0;
     const auto MAX_WIDTH = IMAGE_WIDTH - TEXT_WIDTH;
+    cerr << "Enter block width: ";
+    cin >> BLOCK_WIDTH;
+    bool check = check_width(BLOCK_WIDTH);
+    while (!check) {
+    cerr << "Incorrectly enter. The block width must be >= 3px and <= 30 px. Please try again." << endl;
+    cin >> BLOCK_WIDTH;
+    check = check_width(BLOCK_WIDTH);
+    }
     size_t max_count = 0;
     for (size_t x : bins) {
         if (x > max_count) {
diff --git a/svg_internal.h b/svg_internal.h
new file mode 100644
index 0000000..6b28b0b
--- /dev/null
+++ b/svg_internal.h
@@ -0,0 +1,7 @@
+#ifndef SVG_INTERNAL_H_INCLUDED
+#define SVG_INTERNAL_H_INCLUDED
+
+bool
+check_width(double width);
+
+#endif // SVG_INTERNAL_H_INCLUDED
diff --git a/unittest.cpp b/unittest.cpp
index 5c3f8bd..dbbf756 100644
--- a/unittest.cpp
+++ b/unittest.cpp
@@ -2,6 +2,7 @@
 #define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
 #include "doctest.h"
 #include "histogram_internal.h"
+#include "svg_internal.h"
 
 TEST_CASE("distinct positive numbers") {
     double min = 0;
@@ -52,3 +53,13 @@ TEST_CASE("empty vector") {
     CHECK(min == 0);
     CHECK(max == 0);
 }
+
+TEST_CASE("correct block width") {
+    bool check = check_width(23.5);
+    CHECK(check == true);
+}
+
+TEST_CASE("incorrect block width") {
+    bool check = check_width(59);
+    CHECK(check == false);
+}