Fuel pressure guage

I have the holley electric one mentioned in the previous posts, and a mechanical gauge on the regulator under the hood. The one thing I have noticed on my is the electric does not react to changes to lower pressure as the mechanical does immediately. I had some problems with my fuel system, dirt in the filter and such. one day my pressure at idle was moving up,, I reset the regulator and it again moved... finally pressure dropped low, it showed on the mechanical, put still showed the high reading on the electric unit. thats the only weird thing I have noticed, other than that it works great. Im glad I have the 2 units for conformation.