Open CPN inconsistent with Paper Charts

[Twisted Kilt2]

I've just started using Open CPN on a Mac with OS Catalina version 10.15.7. There was no problem with creating waypoints and routes between San Pedro Harbor and Catalina Island, but I ended up with inconsistencies between what was listed on my route printout for courses between waypoints and what was described when placing the cursor over the legs on the digital chart.
Also, when checking leg courses between the digital chart and Paper chart,
(Maptech #129, Los Angeles & Santa Monica Bay), I found major inconsistencies on course directions. I thought perhaps I wasn't calculating magnetic variations accurately, but found that "True" courses were different as well. Even a plotted position ended up being slightly different on the digital chart compared to the paper position - .4'.
Any suggestions?
Much Appreciated,
Twisted Kilt 2

[bcn]

Which digital chart? RNC or ENC?
Screen shots to understand your findings?
Why do you think that the paper solution is the correct one? What are the differences in degrees? Or tenth of degrees? How do you measure the true course?

[wholybee]

If you are using NOAA charts. Paper charts haven't been updated in a while. This would include "Maptech" branded charts that are printed from official charts. RNC electronic charts are made from the paper charts, and could be expected to be dated as well. The ENC is the current and updated chart. So, if you find discrepancies, the ENC is likely the most correct.

I don't specifically understand what your inconsistencies are, however. Screenshots or examples would help.

[Twisted Kilt2]

Thanks Warren. RNC is the chart currently on my desktop, so I guess I need to figure out how to get the ENC versions up. The compass rose on the RNC chart is consistent with the directions given on the the course legs. Two paper charts I have, one the Maptech and another, an old NOAA of the San Pedro Channel still show differences of about 4 degrees True, which doesn't make sense to me. I'd like to be able to have backup paper in the event that the electronics fail, but I guess I need to get the most current NOAA versions before I start plotting courses from the CPN charts.
Much appreciated,
Mark

[wholybee]

You can download ENC charts in the chart downloader plugin.

I would expect paper and RNC charts of the California coast to all be pretty accurate. But what you might be seeing is that electronic navigation is just more accurate than what you are used to.

What are the issue dates on the paper charts?

[Corsair63]

Have you check if NOAA charts have been printed on WGS84 datum or any of the multiple American Datums?

You should know that if they have been produced with a different datum than WGS84 all plotted position should be shifted in a quantity stated & printed in the chart itself.

[Corsair63]

Also bear in mind that most of the profesional GNSS receivers have the selection of the Datum that you want to use, supposed by default they have activated WGS84, but if you have been using another one to be agreed with the paper charts and not making the correction, now when you want to plot directly , you'll have to switch again to WGS84.

[rooiedirk]

Seems indeed that there are small differeces. I guess rounding errors.