There are almost always some slight differences in totals between the Invoice (which is an aggregation of total approved TimeCards) and any WorkSegment report. These differences, however, should never amount to more than .001% of the total.
The difference is due to the rounding of individual WorkSegments to 2-decimal places. During the week, individual WorkSegments are stored. WorkRecords stores them in 4-decimal places and then displays them to rounded 2 decimals. WorkSegment reports always round the individual segment and then aggregate the total segments. When those 7 days of segments are approved to create a TimeCard (to comply with federal wage laws regarding overtime), each un-rounded WorkSegment is added together for the worker over the 7-day period and then the total is rounded to the nearest 2 decimal places.