Carry-forward errors: how to catch them
Beginning inventory is copied from last period's ending figure. Copy it wrong once and every later period starts from the wrong number, even if everything else is right. The calculator below is prefilled with the slip from the example, so you can see the gap it leaves.
| Expected ending inventory | 184 bbl |
| Gap vs your measured ending | -72 bbl |
Runs in your browser; nothing you type is sent anywhere. Arithmetic for your records, not tax advice.
Worked example: 108 typed as 180
| Period | Correct beginning | Correct ending | Beginning as typed | Ending as typed | Gap |
|---|---|---|---|---|---|
| 1 | 100 | 108 | 100 | 108 | 0 |
| 2 | 108 | 112 | 180 | 184 | 72 |
| 3 | 112 | 108 | 184 | 180 | 72 |
Period 2 produced 60, removed 55 taxpaid and lost 1. Period 3 produced 55, removed 58 and lost 1. The 72 barrel gap never goes away on its own: it rides along until someone corrects the beginning figure.
Three checks that find most slips
- Divide the gap by 9. Swapping two digits always changes a number by a multiple of 9: 180 - 108 = 72 = 8 x 9. If the gap divides evenly by 9, look for transposed digits first.
- Look for a factor of 31. Gallons entered as barrels inflate a figure 31 times; barrels entered as gallons shrink it 31 times. Gallons to barrels has the table.
- Look for a factor of 2 or 6. A keg count typed straight in as barrels is twice too big for half-barrels and six times too big for sixth-barrels.
Prevent it
Compare each period's beginning figure with the prior period's ending figure before you enter anything else, and record a measured ending so the gap is visible at once. Enter the measured figure in the calculator above to see it.
Questions
What is a carry-forward error?
A beginning inventory that does not match the previous period's ending inventory, usually from a typo. It shifts every later period by the same amount until corrected.
How can I tell if a gap is a transposition error?
Swapping two digits changes a number by a multiple of 9, so a gap that divides evenly by 9 often points at transposed digits.