Digital assistant appliance for assisting an operator to manually prepare a liquid pharmaceutical composition in a medical instrument for administering the liquid pharmaceutical composition to a patient; said appliance being characterized in that it comprises: - a user-interface system adapted to indicate manual operations for the operator to perform in manually preparing the liquid pharmaceutical composition and to provide assistance preparation messages corresponding to the manual operations; - a memory device containing data regarding the active principle or principles to be used for the preparation of the liquid pharmaceutical composition, and for each active principle of the liquid pharmaceutical composition: one or more first sample images of vials containing said active principle, and one or more second sample images of syringes to be used for transferring said active principle from the vials to the medical instrument for administering the liquid pharmaceutical composition; - a scale positioned on a horizontal surface; the scale adapted to support a vial or a syringe to be weighed, being manually set on the scale by the operator; - an artificial viewing system designed to acquire: a vial image of a vial manually set by the operator on said scale and a syringe image of a syringe manually set by the operator on said scale; and - an electronic processing system configured to: compare said acquired vial image with each of said first sample images and determine that an incorrect vial has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said first sample images; compare the acquired syringe image with each of said second sample images and determine that an incorrect syringe has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said second sample images; warn the operator of an error condition in the manual composition preparation, through the user-interface system, when the electronic processing system determines that an incorrect vial or syringe manually set on said scale by the operator, is determined by the electronic processing system. - a user-interface system adapted to indicate manual operations for the operator to perform in manually preparing the liquid pharmaceutical composition and to provide assistance preparation messages corresponding to the manual operations; - a memory device containing data regarding the active principle or principles to be used for the preparation of the liquid pharmaceutical composition, and for each active principle of the liquid pharmaceutical composition: one or more first sample images of vials containing said active principle, and one or more second sample images of syringes to be used for transferring said active principle from the vials to the medical instrument for administering the liquid pharmaceutical composition; - a scale positioned on a horizontal surface; the scale adapted to support a vial or a syringe to be weighed, being manually set on the scale by the operator; - an artificial viewing system designed to acquire: a vial image of a vial manually set by the operator on said scale and a syringe image of a syringe manually set by the operator on said scale; and - an electronic processing system configured to: compare said acquired vial image with each of said first sample images and determine that an incorrect vial has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said first sample images; compare the acquired syringe image with each of said second sample images and determine that an incorrect syringe has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said second sample images; warn the operator of an error condition in the manual composition preparation, through the user-interface system, when the electronic processing system determines that an incorrect vial or syringe manually set on said scale by the operator, is determined by the electronic processing system. compare said acquired vial image with each of said first sample images and determine that an incorrect vial has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said first sample images; compare the acquired syringe image with each of said second sample images and determine that an incorrect syringe has been manually set on said scale by the operator, when said acquired vial image does not correspond to any of said second sample images; warn the operator of an error condition in the manual composition preparation, through the user-interface system, when the electronic processing system determines that an incorrect vial or syringe manually set on said scale by the operator, is determined by the electronic processing system.