20. A subpoena shall be in one of Forms 21, 22 or 23 with such variations as circumstances may require. Subpoena for attendance of witness in Chambers. 21. Where a subpoena is required for the attendance of a witness for the purpose of proceedings in Chambers such subpoena, shall issue from the Registry upon the Judge's directive. Correction of error in subpoena 22. In the interval between the issue and service of any subpoena the legal practitioner issuing it may correct any error in the names of parties or witnesses, and may have the writ resealed upon leaving a corrected praecipe of the subpoena marked with the words "altered and resealed", with the signature, name and address of the legal practitioner. Personal service of subpoena. 23. A subpoena shall be served personally unless substituted service has been, ordered by a Judge in a case where a person persistently evades service. The provisions of order 6 of these Rules shall so far as possible apply to service and proof of service of a subpoena. Duration of subpoena. 24. Any subpoena shall remain in force from the date of issue until the trial of the action or matter in which it is issued. Action to perpetuate testimony 25. Any person who would under the circumstances alleged by him to exist become entitled, upon the happening of or any future event, to any honour, title, dignity or office or to any estate or interest in any property, real or personal, the right or claim to which cannot be brought to trial In him before the happening of such event, may commence an action to perpetuate any testimony which may be material for establishing such right or claim. Examination of witness to perpetuate testimony. 26. A witness shall not be examined to perpetuate his testimony unless an action has been commenced for that purpose. Such action not to be set down for trial. 27. No action to perpetuate the testimony of a witness shall be set down for trial. Notice to produce to other party. 28. Where a party to a suit desires any other party to the suit to produce in Court at the trial, a document or any other thing, which he believes to be in the possession or power of that other party, the party desirous of the production shall give "Notice to Produce" to that other party.