Is there any reason why you would need to buy ph 4.0 ? And is it alright just to purchase the ph 7.0 and storage solution for the pen?
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The EC solution also I would purchase. Just don’t understand why the ph 4.0. ?
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You want to know you have atleast two set points when calibrating
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When you calibrate you need at least two calibration points. 7.0 and 4.0 . You can also store it in the 4.0 solution.
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I have both but only use the 7.0. I suppose it’s a bit like triangulation in navigation. Using two set points to determine the accuracy of a third point 
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@Davyg @Bulldognuts thank you for responding.
Will be getting all 3 solutions ph7 ph4 EC storage solution.
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I agree with all above @Ashleyroachclip
Note: I just purchased 7.0 solution last week from Amazon to calibrate my pen (instructions say only need 7.0 solution for midrange measurements but for more accuracy do all 3 points 7.0, 4.0, and 9.0) the solution was testing at 7.7 @ 68 degrees so I had to pick some up at a local grow store.
I have 3 pens and when I went to calibrate the good one it seemed way off so I checked with others to confirm and found the solution way off
After calibrating with new solution tested amazon solution @7.7 with all 3 pens
Here is the one purchased I would stay away from
https://www.amazon.com/gp/product/B0052YE2I0/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
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I’m with you calibration is no better than your solution also need to be careful not to contaminate solution.
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@spankyjr1 I bought biopharma ph 4,7and storage solution. In fact I was looking at that brand and passed on it. Thanks for the heads up.
This is the first time buying these products for my ph tester, Milwaukee 802 3 + 1.
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2 point calibration 4 and 7 basically sets two reference points between the range you will be running in. Equals more accurate reading
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Thanks @kellydans new to all of this, and gets confusing with trying to take it all in. I appreciate the knowledge and support of the people that respond when asked for help…thank you all!
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I’d like to get a blue lab ph tester. I read quite a lot about people not liking the 3 in 1 ph tester . Are they not as accurate and seemed to take and go out of calibration too easy?
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Personally I would not buy a three-in-one Probe, apera or blue lab good quality Meters both around fifty bucks. Cheap Meters you will be chasing calibration every time you use it.( $10 meters )
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Milwaukee 802 $160.00, question when reading it, as I test it,7.10 when put in test solution, but on bottle it reads 7.01 is this the same reading to go by,or should I set meter at 7.0
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Set meter at 7ph same as solution.
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My meter doesn’t calibrate at 7.01 to what is on the test packet that came with the meter. It reads 7.10 , is this the same as 7.1, 7.01 is this 2 different readings?
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Yes you’re correct, 7.1 or 7.10
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Confusing again 
! Thanks when you look at something like that, you expect the meter to read the same as what you’re looking at.
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As long as you get it close you’ll be fine. Sit down with your meter do a couple two point calibrations get comfortable with it. Set 7 pH solution first then go to 4 pH solution. You can’t hurt your Meter. Going back and forth between the two solutions it’s a good habit to rinse probe so you don’t contaminate your solution. Just blow the probe off or dab with cottonball.
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