The Closing Stock (CL STK) is calculated using the formula:

CL STK = OP STK + New Fills – Used Fuel

If both Opening Stock (OP STK) and New Fills are zero, but Used Fuel has a value, the result will naturally be negative. This indicates that fuel consumption is recorded without any available opening stock or refills.

To avoid negative values, ensure that the Opening Stock and New Fills are correctly entered before recording fuel usage. Accurate stock updates will ensure that the Closing Stock reflects the correct balance.