diff --git a/README.md b/README.md
index f2da688..17a900a 100644
--- a/README.md
+++ b/README.md
@@ -1,11 +1,17 @@
 # victor-vc70c-hidraw-reader
-A decoding program for VICTOR VC70C/86C/86D Multimeter as computer device.
-More infomation is included in `vc_hidraw.h`.
+A decoding program for VICTOR VC70C/86C/86D Multimeter as a computer device.
+More information is included in `vc_hidraw.h`.
 
-# Testing
+## Testing
 Use these commands to make sure this program works on your computer with your multimeter connected.
 ```
 git clone https://github.com/wuwbobo2021/victor-vc70c-hidraw-reader/ victor-vc70c-hidraw-reader/
 cd victor-vc70c-hidraw-reader
 sudo make
 ```
+
+## Known Problems
+1. Currently this library is only for Linux platform;
+2. Root authority is required to access the VC70C hidraw device;
+3. `read_vc_multimeter_hidraw(vc_multimeter_reading*)` will block the current thread until next data is received. This may cause inconvenience of using this library.
+4. (minor) When the multimeter is not measuring anything, AC/DC indication in the reading string may be incorrect.
diff --git a/test.cpp b/test.cpp
index 453769d..1651cb4 100644
--- a/test.cpp
+++ b/test.cpp
@@ -1,4 +1,5 @@
 #include <iostream>
+#include "unistd.h"
 #include "vc_hidraw.h"
 
 using namespace std;
@@ -16,7 +17,7 @@ int main(){
 			cout << reading.str << '\n';
 		else {
 			cout << "?\n";
-			sleep(0.1);
+			sleep(0.5);
 		}
 	}
 	
diff --git a/vc_hidraw.c b/vc_hidraw.c
index 4786de6..0e52b38 100644
--- a/vc_hidraw.c
+++ b/vc_hidraw.c
@@ -37,6 +37,9 @@
 
 typedef unsigned char BYTE;
 
+// 0 <= digit <= 7
+#define Byte_Bit(b, digit) ((b >> digit) & 0x01)
+
 const int VC_HID_Vendor_Number = 0x1244;
 const int VC_HID_Product_Number = 0xD237;
 
@@ -93,12 +96,6 @@ const BYTE VC_HID_Digit_Decoding[4][16]
 const BYTE VC_HID_Decimal_Decoding[16] // e+0, 1, 2, 3
 	=  {0, N, N, N, N, N, N, N, 3, N, 2, N, 1, N, N, N};  // buf[0x5], low: 0x4
 
-
-bool byte_bit(BYTE b, BYTE digit){
-	if (digit < 0 || digit > 7) return false;
-	return ((b >> digit) & 0x01);
-}
-
 int vc_fd; bool vc_found;
 
 bool open_vc_multimeter_hidraw(){
@@ -138,8 +135,8 @@ bool read_vc_multimeter_hidraw(vc_multimeter_reading* reading){
 	res = read(vc_fd, buf, HIDRAW_BUFFER_SIZE);
 	if (res < VC_HID_Valid_Buffer_Size) return false;
 	
-	reading->minus = byte_bit(buf[VC_HID_Polarity_Byte], VC_HID_Minus_Bit);
-	reading->AC = ! byte_bit(buf[VC_HID_DCAC_Byte], VC_HID_DC_Bit);
+	reading->minus = Byte_Bit(buf[VC_HID_Polarity_Byte], VC_HID_Minus_Bit);
+	reading->AC = ! Byte_Bit(buf[VC_HID_DCAC_Byte], VC_HID_DC_Bit);
 	
 	reading->str[0] = (reading->minus? '-' : ' ');
 	
@@ -199,8 +196,8 @@ bool read_vc_multimeter_hidraw(vc_multimeter_reading* reading){
 	}
 	
 	BYTE t = buf[VC_HID_Signs_Byte];
-	reading->low_battery_voltage = ! byte_bit(t, VC_HID_Low_Battery_Voltage_Bit);
-	if (! byte_bit(t, VC_HID_Unit_n_Bit)){
+	reading->low_battery_voltage = ! Byte_Bit(t, VC_HID_Low_Battery_Voltage_Bit);
+	if (! Byte_Bit(t, VC_HID_Unit_n_Bit)){
 		reading->value /= 1000*1000*1000;
 		strcat(reading->str, "n");
 	}
diff --git a/vc_hidraw.h b/vc_hidraw.h
index 48d92e1..2707e51 100644
--- a/vc_hidraw.h
+++ b/vc_hidraw.h
@@ -53,12 +53,12 @@ typedef enum vc_multimeter_unit{
 
 typedef struct vc_multimeter_reading{
 	float value;
-	bool minus;
-	vc_multimeter_unit unit;
-	bool AC;
-	bool percent_unit;
-	bool ol; //open-loop
-	bool low_battery_voltage; //battery of multimeter itself
+	vc_multimeter_unit unit : 3; 
+	bool minus : 1;
+	bool AC : 1;
+	bool percent_unit : 1;
+	bool ol : 1; //open-loop
+	bool low_battery_voltage : 1; //battery of multimeter itself
 	
 	char str[21]; // 1 (' ' or '-') + 5 (decimal number) + 1 (' ') + 3 (numeric unit) +
 	              // 3 (unit) + 3 (DC/AC) + 4 (low capacity indication) + 1 ('\0')