In limited cases, the Division may direct self-determination elections to ascertain if certain employees seek to be represented in a larger overall unit. Before directing an add-on election, the Division considers whether: 1) the petition is accompanied by a sufficient showing of interest; 2) there is a sufficient community of interest between the petitioned-for employees and the employees in the unit to which they would be added; 3) the petition includes all similarly-situated employees; and 4) there is a reason why they should be excluded from the larger, overall unit. Brockton School Committee, 26 MLC 191 (2000). In an add-on election, the question before the voters is whether they wish to be represented by the incumbent representative of an existing unit in that unit.