(a) A unitrust rate may not be less than 3 percent, or greater than 5 percent, unless the unitrust plan has been approved by court order. If the unitrust plan has been approved by court order, any unitrust rate may be used. Except as otherwise provided in this subdivision and in paragraph (1) of subdivision (b) of Section 16338, a unitrust rate may be either of the following:
(1) A fixed unitrust interest rate.
(2) A unitrust rate that is determined for each period, using either of the following:
(A) A market index or other published data.
(B) A mathematical blend of market indices or other published data over a stated number of preceding periods.
(b) Except as otherwise provided in subdivision (a) of Section 16335 and paragraph (1) of subdivision (b) of Section 16338, a unitrust plan may provide any of the following:
(1) A limit on how high the unitrust rate determined under paragraph (2) of subdivision (a) may rise.
(2) A limit on how low the unitrust rate determined under paragraph (2) of subdivision (a) may fall.
(3) A limit on how much the unitrust rate determined under paragraph (2) of subdivision (a) may increase over the unitrust rate for the preceding period or a mathematical blend of unitrust rates over a stated number of preceding periods.
(4) A limit on how much the unitrust rate determined under paragraph (2) of subdivision (a) may decrease below the unitrust rate for the preceding period or a mathematical blend of unitrust rates over a stated number of preceding periods.
(5) A mathematical blend of any of the unitrust rates determined under paragraph (2) of subdivision (a) and paragraphs (1) to (4), inclusive, of this subdivision.