I started with one of the cheap yellow pens, it was a nightmare to calibrate. I would put it in 7.0 and calibrate, put it in 4.0 and calibrate.
Back in the 7 to check and it would read 5.8 or something stupid.
So I bought the Hanna and it is rock solid. Once calibrated it is good for a week or 2, I tend to only calibrate if I think it gave me a funny reading and it's always very close to perfect. It may drift to 7.15 or something after a few weeks.
So congrats on starting with a quality pen ☺
You really want the ph4 and ph7 solutions, without them you will never be 100% certain in your mind that its set right. You will get an unexpected reading one day and you will lose your hair worrying about if the pen is calibrated properly or not.
Just buy the solution.
Never cross contaiminate the solutions. I bought 3 small vial type plastic bottles and half fill them with ph7, ph4 and a second ph4 to use for storage, this makes it really easy to use a minimal amount of solution and keeps waste to a minimum. I am still running on my first lot from about 6 weeks ago, the bottles of solution will last me years like this.
So my calibrating method goes like this, I really try not to cross contaminate the ph7 and ph4.
1. Remove the pen from storage solution. Rinse under water. Flick off as much water as possible then with a paper towel dab away any remaining water. Now we have a contaminate free probe ready to calibrate.
2. Put it in the small vial of ph7 and calibrate.
3. Rinse with water and dry it off again
4. Put it in the small vial of ph4 and calibrate.
5. Rinse, dry then go about your measuring.
6. Rinse and dry then put in in the small vial of ph4 storage solution. I use electrical tape to create a seal so it wont spill if knocked over.
Thats it! It might sound like a bit of work but it will give you very accurate results every time and your bottles of solution will last you years.
The golden rule is never put a wet probe into a new solution. Always flick, then dab it dry.