Best way to get input changes in this form?

I am looking for the best method of listening for form changes in this form. It loops through an array adding inputs and I will need to know which specific input has changed so I can save the value. I have started playing with FormArray but not sure the best method of going about this. Any help would be appreciated.

<form [formGroup]="form">
      <ion-row *ngFor="let subQuestion of question.subQuestions; let i = index;">
        <ion-col col-12>
            <ion-input type="text" placeholder="ex: 100" formControlName="value"></ion-input>
            <ion-select interface="popover" formControlName="measurement">
              <ion-option *ngFor="let option of subQuestion.options" value="{{option.value}}">{{option.text}}</ion-option>