Mixing Valve for temp control

[namepending]

In the latest BYO, theres a pretty cool idea about using a mixing valve to control water temps for mash in and sparging. (https://byo.com/stories/issue/item/3147-mixing-valve-projects)

I thought it was a really good idea, but so far have come with one issue. If you're mixing cold (from hose) and hot water (from HLT), how would you determine how much strike water you're putting in the mash tun? Usually I base my mash and strike volumes on the sight tube on my HLT. Maybe I'm over thinking this or missing something. Any comments/ideas?

 

[namepending]

Bumping this old thread to say I ended up making one and it's made life so much easier. I just fill and boil my HLT, not having to worry about stopping at a certain temp. I gravity feed and it's easy to hit my temps dead on. Sure I'd like a HERMS or RIMS setup, but until then, this valve has been great.