2002 D1.1, 6.24.2 says "... Alternative methods may be used for calibrated gain control (attenuator) qualification if proven at least equivalent to 6.30.2." I see no reason another block could not be used. Distance is not the key factor. You are just trying to find a positive indication that when you move the transducer from position "T" to position "U" you get a drop in signal until you get to 40% FSH again. I think the width of the block may be a little bit of a factor so beam spread does not influence. Don't know how you could use IIW or DSC block to perform that verfication though. May need to make your own DS like block.

As for me and my program, when my company told me to gear up to do UT, I put the blocks (IIW, DS, DSC, RS) in my proposed budget for the initial purchase. Decided I did not want to send my machine off to someone else to do what I was capable of doing myself. $400± for the DS block was worth it to be able to verify the machine anytime I wanted to. Part of morning every couple of months is not bad to keep up the verification of the machine. I have performed all my own verifications per D1.1 since we started UT program. See no need to send machine off unless repairs are needed. Have spreadsheets to help with calculations and to print out documentation of verifications. Use Avery stickers to make my own cal stickers although they are readily available online also. Do others in the forum send your machines off periodically or perform your own verifications?