Welf. & Inst. Code, § 1737.1

Whenever any person who has been convicted of a public offense in adult court and committed to and accepted by the Department of the Youth Authority appears to be an improper person to be retained by the department, or to be so incorrigible or so incapable of reformation under the discipline of the department as to render his or her detention detrimental to the interests of the department and the other persons committed thereto, the department may order the return of that person to the committing court. The court may then commit the person to a state prison or sentence him or her to a county jail as provided by law for punishment of the offense of which he or she was convicted. The maximum term of imprisonment for a person committed to a state prison under this section shall be a period equal to the maximum term prescribed by law for the offense of which he or she was convicted less the period during which he or she was under the control of the department. This section shall not apply to commitments from juvenile court.

As used in this section “period during which he or she was under the control of the department” means the period of time during which he or she was physically confined in a state institution by order of the department or the Youth Authority Board.