All promotions of commissioned officers in the organized militia will be made on a best-qualified basis. The officer promotion board will select the best-qualified officer for each promotion from among those officers fully qualified for promotion. To be promoted, the selected officer must also meet the requirements of RCW 38.12.070. In no event will seniority be the sole guideline for selecting the officer to be promoted. The officer promotion board will, in determining the best qualified officer, consider the overall qualifications of an officer and not just the qualifications for one position.