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How blocked and embedded prism is handled on a job depends upon the particular digital calculator and on the equipment being used. Prism can either be incorporated in the design that is ground onto the back surface of the lens, or it can be blocked on a prism blocker, or it can be generated by the generator, or it can be some combination of the three. Note that, unlike a non-digital job, not all generators support grinding prism on a digital job. .
The “Blocker Maximum Prism” “Device max prism” field deserves explanation as it is used for the digital (DS) interface. This parameter does not specify a limit for prism to be included in a design (this is determined by the DS processor itself), rather, it operates as a Y/N switch to specify whether the lab supports blocking prism or not. If set to 0.0, then parameter PBOK=0 is sent to the digital engine, indicating that the lab will not block a maximum of 0 dioptres of prism; any non-zero value will send PBOK=1, indicating that the lab can block some (or all) prism. The amount of prism to be blocked will be sent back to Rx-Universe in the LMS file in the KPRVM parameter. Note that the digital vendor must support the use of PBOK - for some vendors, the setting for prism is controlled (or set) by the calculator, and sending PBOK has absolutely no effect on what the calculator calculates.
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Beginning in version 6.45.00, a flag can be set on the device setup for the generator, indicating whether prism can be sent to the generator for digital jobs.
An example will help illustrate how this works.
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However, if the "Send GPRVM for digital jobs" is not checked, then the job will NOT be sent to the generator, because generating the lens without the required prism would ruin the lens. In this case, the device screen will show "Prsm", and as long as the device is set up to receive a status message, a message will be sent to the generator indicating that "Not all required prism was blocked". The lab may then choose to generator generate the lens on a generator which DOES support grinding the extra prism required.
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