FibreCalc is a basic Optical Fibre parameter calculator. The current version (1.29) calculates and displays around fifteen key parameters of a weakly-guiding step-index single-mode fibre, from Mode Field Radius to Dispersion, taking into account material dispersion. It also plots the field distribution with respect to the RI profile. Calculated parameters include: NA, Delta-N & V-Value; Mode Field Radius (four definitions); Neff and Propagation Constant; Cutoff and Bend Edge Wavelengths; Dispersion and whether Single- or Multi-moded. Input parameters include: Core diameter, Germanium concentration, Wavelength and Core & Clad RI. Output options include: Numerical, Graphical, Save results to file and Save Field Profile to file. The Requirements are as follows. A Palm OS PDA (It is designed to use colour and has only been tested on colour machines. The calculations take around ten seconds on a m505. It would probably be tedious to run them on anything slower. Has been tested on a Palm M505 and a Sony CLIE NZ90.) and HotPaw Basic (Has been tested on version 1.3.1 b0. For HotPaw Basic see http://www.hotpaw.com/rhn/hotpaw). The Details are as follows. Files - The program comprises 13 files that must be placed in the MemoPad and take about 20kb. Calculations - The program calculates a large number of parameters for an optical fibre. It assumes the simplest form of singlemode fibre. The scalar wave equation is solved. Weak guidance is assumed. The calculator only works with circular symmetry and step refractive index profiles. Material absorption is ignored. The program is intended to be handy calculator for those who work with fibre and fibre design. It assumes the user is knowledgeable about fibre specifications and design. Instructions - An Instruction Manual is provided in RTF format.