diff --git a/edfOps.go b/edfOps.go
index f71f43f..c04079f 100644
--- a/edfOps.go
+++ b/edfOps.go
@@ -99,7 +99,8 @@ func (edf Edf) GetDataRecords() int {
 
 // Appends data from one EDF to another. Returns a new EDF object and an error,
 // which is `nil` if everything runs ok. This function requires the
-// EDF files to have the same sampling rate and the same number of channels.
+// EDF files to have the same sampling rate, the same number of channels,
+// and the same duration for each data record.
 //
 // This function is in experimental state and must be used carefully!
 func Append(x, y Edf) (*Edf, error) {
@@ -116,7 +117,7 @@ func Append(x, y Edf) (*Edf, error) {
 	z := NewEdf(x.Header, x.Records)
 
 	// Updating header
-	z.Header["datarecords"] = EnforceSize(strconv.Itoa(x.GetDataRecords() + y.GetDataRecords()), 8)
+	z.Header["datarecords"] = EnforceSize(strconv.Itoa(x.GetDataRecords() + y.GetDataRecords()), GetSpecsLength()["datarecords"])
 
 	// Appending data records
 	for i := 0; i < len(x.Records); i++ {
diff --git a/edfReader.go b/edfReader.go
index 111d06c..987abd1 100644
--- a/edfReader.go
+++ b/edfReader.go
@@ -1,8 +1,10 @@
 package edf
 
-import "os"
-import "bytes"
-import "encoding/binary"
+import (
+	"os"
+	"bytes"
+	"encoding/binary"
+)
 
 /* --- MAIN FUNCTIONS --- */
 
@@ -10,17 +12,17 @@ import "encoding/binary"
 // The header will be a map relating the properties to a string with the raw data
 // The records will be a matrix storing the raw bytes in the file
 func ReadFile(input string) Edf {
-    inlet, err := os.Open(input)
+	inlet, err := os.Open(input)
 
-    if err != nil {
-        panic(err)
-    }
+	if err != nil {
+		panic(err)
+	}
 
-    defer inlet.Close()
-    header := ReadHeader(inlet)
-    records := ReadRecords(inlet, header)
+	defer inlet.Close()
+	header := ReadHeader(inlet)
+	records := ReadRecords(inlet, header)
 
-    return NewEdf(header, records)
+	return NewEdf(header, records)
 }
 
 // Reads the header of an EDF file. Requires the opened EDF file, the list of
@@ -28,100 +30,107 @@ func ReadFile(input string) Edf {
 // the EDF standard. The specs can be accessed though the GetSpecsList
 // function, and their lenghts through the GetSpecsLength one.
 func ReadHeader(inlet *os.File) map[string]string {
-    specsList := GetSpecsList()
-    specsLength := GetSpecsLength()
-    header := make(map[string]string)
-    index := 0
-
-    // Reading header's header
-    for index < len(specsList) {
-        spec := specsList[index]
-
-        if spec == "label" {
-            break
-        } else {
-            data := make([]byte, specsLength[spec])
-            n, _ := inlet.Read(data)
-            header[spec] = string(data[:n])
-        }
-
-        index++
-    }
-
-    // Reading header's records
-    numberSignals := getNumberSignals(header)
-    for index = index; index < len(specsList); index++ {
-        spec := specsList[index]
-        data := make([]byte, specsLength[spec] * numberSignals)
-        n, _ := inlet.Read(data)
-        header[spec] = string(data[:n])
-    }
-
-    return header
+	specsList := GetSpecsList()
+	specsLength := GetSpecsLength()
+	header := make(map[string]string)
+	index := 0
+
+	// Reading header's header
+	for index < len(specsList) {
+		spec := specsList[index]
+
+		if spec == "label" {
+			break
+		} else {
+			data := make([]byte, specsLength[spec])
+			n, _ := inlet.Read(data)
+			header[spec] = string(data[:n])
+		}
+
+		index++
+	}
+
+	// Reading header's records
+	numberSignals := getNumberSignals(header)
+	for index = index; index < len(specsList); index++ {
+		spec := specsList[index]
+		data := make([]byte, specsLength[spec] * numberSignals)
+		n, _ := inlet.Read(data)
+		header[spec] = string(data[:n])
+	}
+
+	return header
 }
 
 // Reads the data records from the EDF file. Its parameters are the pointer to
 // file; and header information, as returned by the ReadHeader function.
 func ReadRecords(inlet *os.File, header map[string]string) [][]int16 {
-    numberSignals := getNumberSignals(header)
-    numberSamples := getNumberSamples(header)
-    records := make([][]int16, numberSignals)
-    sampling := make([]int, numberSignals)
-    duration := str2int(header["duration"])
-    dataRecords := str2int(header["datarecords"])
-
-    // setup records
-    for i := 0; i < numberSignals; i++ {
-        sampling[i] = duration * numberSamples[i]
-        records[i] = make([]int16, sampling[i])
-    }
-
-    // translate data
-    for d := 0; d < dataRecords; d++ {
-        for i := 0; i < numberSignals; i++ {
-            data := make([]byte, 2*sampling[i])
-            inlet.Read(data)
-            records[i] = appendInt16Arrays(records[i], translate(data))
-        }
-    }
-
-    return records
+	numberSignals := getNumberSignals(header)
+	numberSamples := getNumberSamples(header)
+	records := make([][]int16, numberSignals)
+	sampling := make([]int, numberSignals)
+	duration := str2int(header["duration"])
+	dataRecords := str2int(header["datarecords"])
+
+	// setup records
+	for i := 0; i < numberSignals; i++ {
+		sampling[i] = duration * numberSamples[i]
+		records[i] = make([]int16, sampling[i])
+	}
+
+	// Reading records
+	dataRecordsSize := 2 * dataRecords * Sigma(sampling)
+	data := make([]byte, dataRecordsSize)
+	inlet.Read(data)
+
+	// translate data
+	i := 0
+	for d := 0; d < dataRecords; d++ {
+		for s := 0; s < numberSignals; s++ {
+			step := 2*sampling[s]
+			piece := data[i:i+step]
+			records[s] = appendInt16Arrays(records[s], translate(piece))
+			i += step
+		}
+	}
+
+	return records
 }
 
 
 /* --- AUXILIAR FUNCTIONS --- */
 func translate(inlet []byte) []int16 {
-    var data int16
-    limit := len(inlet)/2
-    outlet := make([]int16, limit)
-    buffer := bytes.NewReader(inlet)
-
-    for i := 0; i < limit; i++ {
-        // oops := binary.Read(buffer, binary.BigEndian, &data)
-        oops := binary.Read(buffer, binary.LittleEndian, &data)
-        if oops == nil {
-            outlet[i] = data
-        } else {
-            panic(oops)
-        }
-    }
-
-    return outlet
+	var data int16
+	limit := len(inlet)/2
+	outlet := make([]int16, limit)
+	buffer := bytes.NewReader(inlet)
+
+	for i := 0; i < limit; i++ {
+		// oops := binary.Read(buffer, binary.BigEndian, &data)
+		oops := binary.Read(buffer, binary.LittleEndian, &data)
+		if oops == nil {
+			outlet[i] = data
+		} else {
+			panic(oops)
+		}
+	}
+
+	return outlet
 }
 
 func getNumberSignals(header map[string]string) int {
-    raw := header["numbersignals"]
-    return str2int(raw)
+	raw := header["numbersignals"]
+	return str2int(raw)
 }
 
 func getNumberSamples(header map[string]string) []int {
-    numberSignals := getNumberSignals(header)
-    numberSamples := make([]int, numberSignals)
-    samples := separateString(header["samplesrecord"], numberSignals)
+	numberSignals := getNumberSignals(header)
+	numberSamples := make([]int, numberSignals)
+	samples := separateString(header["samplesrecord"], numberSignals)
 
-    for i := 0; i < numberSignals; i++ {
-        numberSamples[i] = str2int(samples[i])
-    }
+	for i := 0; i < numberSignals; i++ {
+		numberSamples[i] = str2int(samples[i])
+	}
 
-    return numberSamples
+	return numberSamples
 }
diff --git a/useful.go b/useful.go
index c5eac7d..883ce57 100644
--- a/useful.go
+++ b/useful.go
@@ -148,3 +148,12 @@ func EnforceSize(field string, limit int) string {
 
 	return field
 }
+
+// Sums all values of an int array
+func Sigma(a []int) int {
+	r := 0
+	for i := 0; i < len(a); i++ {
+		r += a[i]
+	}
+	return r
+}
\ No newline at end of file