A user interface for a sonographic device is disclosed that displays a sonographic image and at least one reference object corresponding to a catheter size. The reference object may be scaled in proportion to the sonographic image. In addition, the user interface may further display a plurality of vertical lines and a plurality of horizontal lines arranged in a grid-like pattern and placed over the sonographic image. The size of both the sonographic image and the at least one reference object may change in proportion to a chosen insertion depth. A display device, a sonographic device and corresponding methods are also disclosed.