G24 - Walton & Beckett, ratio 5:1, different diameters

Walton and Beckett Graticule for Asbestos - G24

Calibration factors are required for each of these graticules. See note below.

The Walton and Beckett graticule is used for counting fibrous dust (e.g. asbestos or glass fibers) and is particularly useful where the majority of fibers to be counted are shorter than 5 microns. The circle is divided into four by two diametrical lines scaled in units of 5 and 3 microns respectively. 3 and 5 microns are the critical measurements of fiber lengths and diameters used in fiber counting. Unlike the usual globes of other particle graticules, the Walton and Beckett have a series of shapes to compare objects with. These shapes have been designed for comparison with fibers, especially since they incorporate an aspect ratio of 3:1 or 5:1 essential for such analysis.

IMPORTANT NOTE: The circle on these Walton & Beckett graticules must represent 100 microns at the stage and each one must be manufactured to suit the individual instrument.

All Walton & Beckett reticles are normally used with 40x objectives giving a calibration factor of 4. In some microscopes
there is also an additional 1.25x magnification to give a total objective magnification of 50x - these will have a calibration
factor of 5. All standard Walton & Beckett reticles are supplied with a calibration factor of 4. Other calibration factors are
made to special order. These reticles will require a calibrated stage micrometer to verify the sizes - e.g. S12 or PS12.

Therefore, details should be provided with your order of:

1. Calibration factor, if known;
2. Objective magnification;
3. Eyepiece magnification;
4. Diameter of graticule disc required;
5. Microscope make and model.