serial plotter doesnt work!

hi I'm using a TCRT5000 module , and I can't see anything in serial plotter... here is the code:

int a,b,now,before;
void setup() 
{
Serial.begin(9600);
pinMode(6,OUTPUT);
before= 0;
}

void loop() {
 now= 0;
 digitalWrite(6,HIGH);    // Turning ON LED
 delay(20);  //wait
 a=analogRead(A3);        //take reading from photodiode(pin A3) :noise+signal
 digitalWrite(6,LOW);     //turn Off LED
 delay(20);  //wait
 b=analogRead(A3);        // again take reading from photodiode :noise
 now=a-b;                    //taking differnce:[ (noise+signal)-(noise)] just signal
 Serial.print(now/before);         // denoised signal
 Serial.println("%");
 before=now;
}

This line:

R0UGH: Serial.println("%");

The plotter sees the number and the % next to each other as a text string and so ignores it. The best thing is to remove that. If you're set on having the %, then add a space between the number and the %. That will work as you expect, but the legend in Serial Plotter will show that there are two lines, even though only the first is plotted, since the second never provides any valid numerical values.