The ROUND function limits your numbers to 2 decimal places and is causing the inaccuracy. Change the round functions to use 3 decimal places to add precision.

Then change the TEXT function for the seconds part to output the values as 00.0.

Here is the updated function.

Then change the TEXT function for the seconds part to output the values as 00.0.

Here is the updated function.

```
=CONCATENATE(TEXT(INT(ABS(A2)),"000"),":",TEXT(INT(ROUND(MOD(ABS(A2),1),3)*60),"00"),":",TEXT(ROUND(MOD(ROUND(MOD(ABS(A2),1),3)*60,1),3)*60,"00.0"),":",IF(A2<0,"S","N"),"/",TEXT(INT(ABS(J2)),"000"),":",TEXT(INT(ROUND(MOD(ABS(J2),1),3)*60),"00"),":",TEXT(ROUND(MOD(ROUND(MOD(ABS(J2),1),3)*60,1),3)*60,"00.0"),":",IF(J2<0,"W","E"))
```