Tom,
There are so many variables; John's point about jumpers, perhaps a 
bit of wild RF floating around plus the five percent variability of 
the meter, and probably a lot more inconsistiencies.  I think that 
the TW1 is a fine device for tracking SWR, and the rest is a 
bonus.  And at the end of the day it is still ham radio and fun.
Pat, K9JAUAt 05:57 AM 12/13/2012, you wrote:
>Hey, all.
>
>As I have addressed my most recent issue with the TS590 DC power cable, I
>have noticed something interesting with my TW1 swr/watt meter.
>
>Actually, I thought I already knew this, but my most recent readings have
>reminded me of the issue.
>
>Now, with both of my TS590 power cables, when the rig is set to 100 watts
>output, I consistently get 100 watts as a power reading on the TS590's
>internal meter.
>
>However, when using the LDG TW1 talking watt meter, my readings can vary
>anywhere from 85 to 91 watts, with occasional dips as low as 81 watts.
>
>Keep in mind that all of these readings are taken on a resonant frequency
>with my Alpha Delta DXCC antenna and an SWR of 1.0 to 1.  Also, I get the
>same reading variations with the TW1 when using a dummy load.
>
>I checked the TW1 manual, and they clame an accuracy of plus or minus 5
>percent on 14 mhz, but I think that is debatable.
>
>On the other hand, do we know how accurate the TS590's power meter is as
>well?
>
>I'm not one to quibble over 10 or 15 watts, but I find the inconsistent
>readings with the TW1 to be at least interesting.
>
>73 from Tom Behler: KB8TYJ