[数值问题] 如何提高精度？

PROGRAM MAIN 
   
 IMPLICIT NONE
 INTEGER I 
REAL T  
REAL  CCU,CNBSN 
REAL RES        
REAL*8 ACU,ASC  
REAL B,RRR  
REAL CAV 
REAL  t1,t2 
REAL*16  Q,F 
REAL y   
REAL Iop  
 F=0.000
 
 t1=0.0 
 Iop=8930.0 
 B=12.84
 RRR=150
 ACU=3.80233E-5 
 ASC=3.80233E-5
 t2=2.0
 y=5.0
 Q=Iop**2*y*(EXP(-2.0*y*t1/2.0)-EXP(-2.0*y*t2/2.0)) &
              /(2.0*Acu**2.0)
 WRITE(*,*) "Q=",Q
 DO I=1,11  
     T=89.0+(i-1)*0.1
     CALL CNB3SN(T,B,CNBSN)
     CALL CCCU(T,CCU)
     CALL DIANZULV(T,B,RRR,RES) 
     CAV=(CCU*ACU+CNBSN*ASC)/(ACU+ASC) 
      F=CAV*0.001/RES+F
END DO
STOP
END
    

SUBROUTINE CNB3SN(T,B,CNBSN)
IMPLICIT NONE
REAL   b4,b3,b2,b1,b0
REAL  T,B
REAL  CNBSN
   IF(T>0.0  .AND.  T<10.4 ) THEN
           b4=0.0
           b3=38.8-1.8*B+0.0634*B**2
           b2=-110*exp(-0.434*B)
           b1=207.0-3.83*B+2.86*B**2
           b0=0
         
   ELSEIF(T>10.4  .AND.  T<26.113 ) THEN    
           b4=0.0
           b3=7.42
           b2=0.0
           b1=1522.0
           b0=0.0
  ELSEIF(T>=26.113 .AND. T<169.416) THEN 
           b4=0.0
           b3=0.0
           b2=-61.635
           b1=19902.0
           b0=-305807.0 
  ELSEIF(T>=169.416 .AND. T<300.0) THEN  
           b4=0.0
           b3=0.0
           b2=-7.4636
           b1=4411.0
           b0=763801.0
  ELSE
             b4=0.0
             b3=0.0
             b2=0.0
             b1=0.0
             b0=1415377.0
  ENDIF
         CNBSN=b4*(T**4)+b3*(T**3)+b2*(T**2)+b1*T+b0
  RETURN
  END   
SUBROUTINE CCCU(T,CCU)
IMPLICIT NONE
REAL a0,a1,a2,a3,a4,a5,a6,a7
REAL dens,aa1,aa2,aa3,aa4,aa
REAL T
REAL CCU
a0=-1.91844
a1=-0.15973
a2=8.61013
a3=-18.996
a4=21.9661
a5=-12.7328
a6=3.54322
a7=-0.3797
aa1=a0*((log10(T))**0.0)+a1*((log10(T))**1.0)
aa2=a2*((log10(T))**2.0)+a3*((log10(T))**3.0)
aa3=a4*((log10(T))**4.0)+a5*((log10(T))**5.0)   
aa4=a6*((log10(T))**6.0)+a7*((log10(T))**7.0)
aa=aa1+aa2+aa3+aa4 
dens=8960.0  
  CCU=dens*(10.0**aa)*1.0
 WRITE(*,*) "CCU=",CCU
 RETURN
 END
    
   
SUBROUTINE DIANZULV(T,B,RRR,RES)    
REAL RES1,RES2,RES3,RES
    RES1=1.7E-8/RRR
    RES2=1.0E-8/(2.33*10**9/T**5+9.57*10**5/T**3+163.0/T)
    RES3=(0.37E-10+0.0005E-10*RRR)*B
    RES=RES1+RES2+RES3
    RETURN
    END