I created an Excel spreadsheet to calculate how much rode to let out for different scopes for different depths, based on my boat.
Here is a screen shot of it:
You can see the formula that I used near the top in the formula window: =((A3 + 2)*3)+3-25
A3 = water depth; the first '2' = the depth of my transducer below the water surface (it's actually closer to 1 ft down, but this adds just a little safety margin); the '3' is the desired scope i.e. 3:1 - for 5:1 scope, this number would be 5 etc.; the '25' is the length of chain I have at the end of my rode.
The depth actually goes down to 90', but I only took a screen shot of the top portion of the page.
I printed this and there is a copy in my chain locker. That way when the anchor is set my crew only needs to know the depth and the desired scope and can let out the proper amount of rode without doing a lot of mental calisthenics.
I also played around and created a rode calculator that can be be used for any boat:
Just put in your boat's info, depth and desired scope and it tells you how much rode to let out.
I'm sure after a while, with more experience, this 'training wheel' won't be required, but I found it very useful.
Let me know what you think.