It shall be the duty of the board of equalization to meet on the second Monday in March and sit as long as may be necessary to carefully examine and inspect all tax returns and assessments delivered to it by the county tax assessor. If the board finds that any taxpayer has neglected to make a return or has omitted from his return any property that should be returned, it shall be its duty to make up a return upon the proper blank with a description of the property to be assessed, which property it shall then proceed to value and equalize in the same manner as other property is valued and equalized by it, and to the value thus placed thereon shall be added a penalty of 10 percent for failure of the owner of such property to properly return the same. The secretary of the board shall by certified or registered mail, return receipt demanded, or in person give notice to the owner of any property which has been omitted from the tax return and has been assessed as provided in this section.