This means that the income from the lowest-paying job is more than 50% that of the highest-paying. The IRS indicates that checking box c will result in a more accurate withholding if the lowest household income is more than half the highest salary.
For example:
you are a single filer with two jobs with taxable annual incomes of $82,000 and $21,000 on your previous year's W2s. Using the page 4 chart that corresponds with your filing status, you would enter $5,040 on line 1 of the worksheet.
Thanks for joining the event today, Net miller!