gistfile1.m

    RACSignal *latest = [RACSignal combineLatest:@[ self.maxWeightTextField.rac_textSignal, self.maxRepsTextField.rac_textSignal ]];
    [latest subscribeNext:^(RACTuple *values) {
       
        RACTupleUnpack(NSString *maxWeight, NSString *maxReps) = values;
        
        CGFloat maxWeightValue = maxWeight.floatValue;
        NSInteger repIndex = maxReps.integerValue;
        
        CGFloat percentages[12] = {
          
            1.00f,
            0.95f,
            0.90f,
            0.88f,
            0.86f,
            0.83f,
            0.80f,
            0.78f,
            0.76f,
            0.75f,
            0.72f,
            0.70f
        };
        
        repIndex = MAX(1, repIndex);
        repIndex = MIN(12, repIndex);
        
        CGFloat percentage = percentages[repIndex - 1];
        
        CGFloat oneRepMax = maxWeightValue / percentage;
        self.oneRepMaxTextField.text = [NSString stringWithFormat:@"%.02f", oneRepMax];
    }];