Default Variance Account

I'm trying to understand what has caused variances that default to "Variances Default" account. I can look at LabDtl for scrap reason but nothing really to explain material content? I've also, looked at the Job files and can only find total volume expected against actual but this doesn't relate back to the labour transactions, or that I can find? Anyone out there got any good ideas how can achieve this without making a mega report linking several huge files together?