I’m using I2C OLED , ESP8266 nodemcu and Pulse Sensor.
I get the wrong reading Every time I put my finger on top of the pulse sensor.
Also, the sensor keeps displaying reading without touch the sensor. 
Could you help me?

#include <Adafruit_SSD1306.h>
#define OLED_Address 0x3C // 0x3C device address of I2C OLED. Few other OLED has 0x3D
Adafruit_SSD1306 oled(128, 64); // create our screen object setting resolution to 128×64

int a=0;
int lasta=0;
int lastb=0;
int LastTime=0;
int ThisTime;
bool BPMTiming=false;
bool BeatComplete=false;
int BPM=0;
#define UpperThreshold 550
#define LowerThreshold 500

void setup() {
oled.begin(SSD1306_SWITCHCAPVCC, OLED_Address);
oled.clearDisplay();
oled.setTextSize(2);
}

void loop()
{
if(a>127)
{
oled.clearDisplay();
a=0;
lasta=a;
}

ThisTime=millis();
int value=analogRead(0);
oled.setTextColor(WHITE);
int b=60-(value/16);
oled.writeLine(lasta,lastb,a,b,WHITE);
lastb=b;
lasta=a;

if(value>UpperThreshold)
{
if(BeatComplete)
{
BPM=ThisTime-LastTime;
BPM=int(60/(float(BPM)/1000));
BPMTiming=false;
BeatComplete=false;
//tone(8,1000,250);
}
if(BPMTiming==false)
{
LastTime=millis();
BPMTiming=true;
}
}
if((value<LowerThreshold)&(BPMTiming))
BeatComplete=true;

oled.writeFillRect(0,50,128,16,BLACK);
oled.setCursor(0,50);
oled.print(“BPM:”);
oled.print(BPM);

oled.display();
a++;
}