They do not exist because there is no reason for them to other than as a toy. The level of accuracy you think you need, you do not and an analog gauge provides information at a passing glance rather than having to actually stop and read the numbers. Many divers would need glasses to see a digital readout but can see the needle position on their analog gauge just fine. There is no advantage in reliability, in fact a serious reduction due to the need for a battery and a sealed electronic compartment. A mechanical spg will continue to read even if flooded though higher by the difference of ambient minus sea level pressure.
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