diff --git a/col.go b/col.go
index 13d5ad7..52b412f 100644
--- a/col.go
+++ b/col.go
@@ -54,7 +54,15 @@ func (xf *XfRk) String(wb *WorkBook) string {
 		fNo := wb.Xfs[idx].formatNo()
 		if fNo >= 164 { // user defined format
 			if formatter := wb.Formats[fNo]; formatter != nil {
-				if strings.Contains(formatter.str, "#") || strings.Contains(formatter.str, ".00") {
+				formatterLower := strings.ToLower(formatter.str)
+				if formatterLower == "general" ||
+					strings.Contains(formatter.str, "#") ||
+					strings.Contains(formatter.str, ".00") ||
+					strings.Contains(formatterLower, "mm/yy") ||
+					strings.Contains(formatterLower, "dd/yy") ||
+					strings.Contains(formatterLower, "mm.yy") ||
+					strings.Contains(formatterLower, "dd.yy") ||
+					strings.Contains(formatterLower, "дд.гг") {
 					//If format contains # or .00 then this is a number
 					return xf.Rk.String()
 				} else {
diff --git a/comparexlsxlsx.go b/comparexlsxlsx.go
index 080f50a..eab82b2 100644
--- a/comparexlsxlsx.go
+++ b/comparexlsxlsx.go
@@ -3,17 +3,18 @@ package xls
 import (
 	"fmt"
 	"github.com/tealeg/xlsx"
-	"path"
+	"math"
+	"strconv"
 )
 
 //Compares xls and xlsx files
-func compareXlsXlsx(filepathname string) string {
-	xlsFile, err := Open(path.Join("testdata", filepathname)+".xls", "utf-8")
+func compareXlsXlsx(xlsfilepathname string, xlsxfilepathname string) string {
+	xlsFile, err := Open(xlsfilepathname, "utf-8")
 	if err != nil {
 		return fmt.Sprintf("Cant open xls file: %s", err)
 	}
 
-	xlsxFile, err := xlsx.OpenFile(path.Join("testdata", filepathname) + ".xlsx")
+	xlsxFile, err := xlsx.OpenFile(xlsxfilepathname)
 	if err != nil {
 		return fmt.Sprintf("Cant open xlsx file: %s", err)
 	}
@@ -29,8 +30,22 @@ func compareXlsXlsx(filepathname string) string {
 				xlsText := xlsRow.Col(cell)
 				xlsxText := xlsxCell.String()
 				if xlsText != xlsxText {
-					return fmt.Sprintf("Sheet: %d, row: %d, col: %d, xlsx: (%s)[%d], xls: (%s)[%d].",
-						sheet, row, cell, xlsxText, len(xlsxText), xlsText, len(xlsText))
+					//try to convert to numbers
+					xlsFloat, xlsErr := strconv.ParseFloat(xlsText, 64)
+					xlsxFloat, xlsxErr := strconv.ParseFloat(xlsxText, 64)
+					//check if numbers have no significant difference
+					if xlsErr == nil && xlsxErr == nil {
+						diff := math.Abs(xlsFloat - xlsxFloat)
+						if diff > 0.0000001 {
+							return fmt.Sprintf("sheet:%d, row/col: %d/%d, xlsx: (%s)[%d], xls: (%s)[%d], numbers difference: %f.",
+								sheet, row, cell, xlsxText, len(xlsxText),
+								xlsText, len(xlsText), diff)
+						}
+					} else {
+						return fmt.Sprintf("sheet:%d, row/col: %d/%d, xlsx: (%s)[%d], xls: (%s)[%d].",
+							sheet, row, cell, xlsxText, len(xlsxText),
+							xlsText, len(xlsText))
+					}
 				}
 			}
 		}
diff --git a/issue47_test.go b/issue47_test.go
index ab5a713..098604d 100644
--- a/issue47_test.go
+++ b/issue47_test.go
@@ -1,14 +1,30 @@
 package xls
 
 import (
+	"io/ioutil"
+	"path"
+	"path/filepath"
+	"strings"
 	"testing"
 )
 
 func TestIssue47(t *testing.T) {
-	e := compareXlsXlsx("issue47")
+	testdatapath := "testdata"
+	files, err := ioutil.ReadDir(testdatapath)
+	if err != nil {
+		t.Fatalf("Cant read testdata directory contents: %s", err)
+	}
+	for _, f := range files {
+		if filepath.Ext(f.Name()) == ".xls" {
+			xlsfilename := f.Name()
+			xlsxfilename := strings.TrimSuffix(xlsfilename, filepath.Ext(xlsfilename)) + ".xlsx"
+			err := compareXlsXlsx(path.Join(testdatapath, xlsfilename),
+				path.Join(testdatapath, xlsxfilename))
+			if err != "" {
+				t.Fatalf("XLS file %s an XLSX file are not equal: %s", xlsfilename, err)
+			}
 
-	if e != "" {
-		t.Fatalf("XLS an XLSX are not equal: %s", e)
+		}
 	}
 
 }
diff --git a/testdata/negatives.xls b/testdata/negatives.xls
new file mode 100644
index 0000000..47902e3
Binary files /dev/null and b/testdata/negatives.xls differ
diff --git a/testdata/negatives.xlsx b/testdata/negatives.xlsx
new file mode 100644
index 0000000..0d705cc
Binary files /dev/null and b/testdata/negatives.xlsx differ
diff --git a/testdata/superstore.xls b/testdata/superstore.xls
new file mode 100644
index 0000000..34c7090
Binary files /dev/null and b/testdata/superstore.xls differ
diff --git a/testdata/superstore.xlsx b/testdata/superstore.xlsx
new file mode 100644
index 0000000..b610f26
Binary files /dev/null and b/testdata/superstore.xlsx differ