Hi Houghy,
Congratulations on the 16"Lb. It is a great buy at the price, especially with all the extras!!
There is a formula to counter weight dobs.
It's roughly 2.5X the weight at the mirror end, to what you're placing at the e/p end.
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I have a shroud, 9x50mm finder, and a dew/light shield for my 12".
The total c/w needed is 3.8kg.
If you have other questions, please ask.