Operation manual of ZBL-R800, ZBL-R630, ZBL-C310AHotline: (86)010-51290405 Fax: (86)010-5129040655diameter value. If the thickness value is less than the minimum valuein table 3.2, “Too small” will be shown in the instrument and if it isabove the maximum value in table 3.2, “Too large” will be displayed ,at that time, rebar diameter cannot be measured.During measurement, when the thickness of cover is too small, it isrecommended that a PMMA(or other non-metallic materials) ispadded under sensor, the measured value minus the thickness of pad isthe tested thickness of cover.3.5 Introduction of rust test3.5.1 Main menu of rust testPressing【a】,【b】and【_】 key to select “Rust Test”, then pressing【ENTER】to enter into rust test main menu as shown in figure3-39.Figure 3-39 Main menu of rust testIn the main menu, user can set parameters such as object No., testingmethod etc., also can check or delete the stored data. Uniformprinciple for menu operation is:1. Pressing 【a】or【b】to select different menu options.2. Pressing【ENTER】to enter into current option.3. Pressing【MENU】to go back to menu selection state.4. Pressing【BACK】to go back to previous state.5. Pressing【SAVE】to store parameter setting.