Arduino Uno + KTY81/210 temperature sensor

hi,

sorry, new , unsure lot of things, need clarification. haven't found information explains how , why things work, "do this, that"

i following guide (arduino-thermistor-temperature-sensor-tutorial) connect thermistor arduino uno.

here temperature sensor information:

temp. sensor 2000r +-1% to92
part.no.:   kty81-210
name:   temp. sensor 2000r +-1% to92
description:   2.5mm, 1980...2020ohm, -55...+150°c

and here sensor's data-sheet: sensor data-sheet

i have connected same way in guide. works , values being serial printed.

what don't understand:

1. thermistor's , resistor's ohm value should equal, correct? in case 2000 ohm?
2. thermistor has ptc, i'm guessing have invert math or use ntc thermistor instead correct values? (currently resistance goes temperature goes down)
3. understand code uses steinhart-hart math logic convert resistor value temperature value, need a, b , c coefficients of thermistor equation. don't understand how them data-sheet. take 3 temperature , corresponding resistance values, put them in calculator , use resulting coefficients?

thanks in advance.

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