You should never stick your finger in the soil, especially an inch deep lest you disturb the roots and contaminate the soil. I don't like moisture meters because they require you to puncture the soil, thus disturbance and you lessen the amount of grow room for roots and you already have limited space with a dixie cup.
I suggest to pick it up and if it feels light and the surface appears dry then water it until the soil stops sucking down the water after about a second. I suggest you literally spoon feed the plant its water so that you will never over water your plants and you can also get a feel for how much you need.
Cut holes in the bottom if you haven't already, just in case you slip up and do over water it, because the water will just drain out, but this is bad.
You should never give your plant so much water that it finds water near the bottom or sides of your vessel. You will cause root bound and hurt the growth of your plant and even kill it as it tangles its self.
Just give it a little at a time, just near the base of the stem and out about .5 to 1.0 inches in diameter and you should be OK.
