(99)The requirements of this Regulation should be applicable to all devices placed on the market or put into service from the date of application of this Regulation. However, in order to provide for a smooth transition it should be possible, for a limited period of time from that date, for devices to be placed on the market or put into service by virtue of a valid certificate issued pursuant to Directive 90/385/EEC or pursuant to Directive 93/42/EEC.