Geometric design and strength check of internal spur gear with straight and helical toothing. Application is developed in MS Excel is multi-language and supports Imperial and Metric units and solves the following main tasks: - Calculation of helical and straight toothing (internal). - Automatic design of a transmission with the minimum number of input requirements. - Design for entered coefficients of safety (static dynamic). - Calculation of complete geometric parameters (including corrected toothing). - Optimization of toothing by use of proper correction (balancing specific slips miminizing specific slips strength...). - Calculation of strength parameters safety check. - Design of gearing for exact axis distance. - Supplementary calculations (calculation of parameters of the existing gear temperature rise design of shafts check dimensions). - Support of 2D and 3D CAD systems. - Drawings of an accurate tooth shape including data (XY coordinates). - Support of 2D CAD (AutoCAD AutoCAD LT IntelliCAD Ashlar Graphite TurboCAD) and 3D CAD in full calculation package (Autodesk Inventor SolidWorks SolidEdge Pro/E). The calculations use procedures algorithms and data from standards ANSI ISO DIN BS and specialized literature. Used standards: ISO 6336 ISO 1328 DIN 3990 ANSI B6.1-1968 AGMA 2001-C95 AGMA 2001-D04 AGMA 908-B89/95 and others.This module is a part of MITCalc - Mechanical and Technical Calculation Package for gear belt and chain drives springs beam shaft bolt connection shaft connection tolerances and many others