Differences in Electronic and paper dive tables

[drhemi70]

All,
First post.
Here is the problem I was trying to to calculate surface interval times using both tabls and the erdp here is what I can across.
1st dive to 75 ft with 25 min abt, second dive to 75 ft with 25 min abt.
The paper tablet (standard) says surface interval should be about 2:20 while the erdp says an 1:26. Here are my questions?
Has anyone else seen these differences between the paper and electronic rdp? Second is the electronic rdp accounting for two 15 ft stops? Third would two 15 ft 3-5 min stops account for a 1 hour difference in surface interval.
I appreciate your answers and look forward to the discussion.

Dive Safe,
DR

 

[Blackwood]

I don't know for sure, but maybe the eRDP is calculating at 75 feet whereas per PADI's table methodology that would be an 80 foot dive.

My question to you (before I can really address yours) is: what's the goal of your surface interval? 2:20 or 1:26 before what? A certain letter group?

 

[DBailey]

I don't have either in front of me, but my guess is that the eRDP figures the dives at intervals smaller than 10 feet in depth. Rather than rounding up to 80 that you'll need on the table.

Your safety stops at 15 feet do not affect your pressure groups; therefore, they do not affect the surface interval.

Edit: I found a eRDP online and an RDP.

For the RDP card, you have to round up to 80 feet for both dives. On the eRDP, you get to use the exact 75 feet without rounding.

If you try to extrapolate 75 from the table (values halfway between 70 and 80) which isn't a valid planning tool, but it helps for comparison in this situation, I came up with a minimum surface interval of 1h 5m. So the eRDP appears to be using exactly 75 feet.

This is a great example of how conservative the tables are due to the rounding that can occur.

 

[drhemi70]

No I am not shooting for a certain letter group, it was a theroy question brought up in class to help estimate how long a diver would be gone and when he could tell his wife he would be home. The reason for me asking it here is if there is something off with the erdp and it is giving 1 hour shorter surface intervals I would think this could be potentially dangerous information to follow considering that you would not off gas as much nitro and could be increasing your risk of narcosis or getting bent.
DR

 

[JohnB47]

I concur with DBailey.

 

[dwhthediver]

The yellow eRDP or the blue eRDPml? The blue one(ml) is actually an electronic wheel, and as such uses 5' increments which will give you a difference