Google 'room temperature app'. There's quite a few actually. My MIL has a digital outdoor thermometer and I tested a couple of the 4star apps vrs it. All 3 were within 2°F. However, area tested vrs environment is a concern. Hanging wallclocks and ac controls are at certain heights,either within certain ranges of heat/cool sources or vents and placement of such can and will change the temp. Ie. In a heated room, it's warmer closer to the ceiling, in an air conditioned room its cooler towards the floor. It can be warmer closer to sun facing exterior walls in summer or cooler towards shade facing walls in winter. A 5°F change in temp is easy to attain between areas. Your room is not all one single ambient temp, but variegated in layers and areas. And that's not including the mess that a ceiling fan makes of things.
To get a somewhat accurate reading of ambient temps, according to the pc, you'll need to stick the thermometer about a foot away from the intake fans, at about the same level.