Getting strange behaviour when value goes above 10?

[Alifar]

See image, why am I getting this behaviour when it goes up 10?

See my code below:

float n = [[sort objectAtIndex:0] floatValue];
        
        NSString* forFloat = [NSString stringWithFormat:@"%.3f", n];
        lowFloat = [forFloat floatValue]-0.001;

NSMutableArray* chartData = [NSMutableArray arrayWithCapacity:self.lineData.count];
            NSMutableArray* months = [NSMutableArray arrayWithCapacity:self.lineData.count];
            for(int i=0;i<self.lineData.count;i++) {
                
                Kobject *z = [self.lineData objectAtIndex:i];
                chartData[i] = [NSNumber numberWithFloat:[z.oPrice floatValue]-lowFloat];
                months[i] = z.oDate;
            }
            
            self.lineChart = [[FSLineChart alloc] initWithFrame:CGRectMake(15, 44, [UIScreen mainScreen].bounds.size.width - 30, 120)];
            self.lineChart.verticalGridStep = 6;
            self.lineChart.horizontalGridStep = 7;
            self.lineChart.fillColor = [UIColor colorWithRed:0.24 green:0.72 blue:0.68 alpha:0.20];
            self.lineChart.color = [self.lineChart.dataPointColor colorWithAlphaComponent:0.3];
            self.lineChart.valueLabelPosition = ValueLabelLeftMirrored;
            self.lineChart.indexLabelFont = [UIFont fontWithName:@"HelveticaNeue-Light" size:10];
            self.lineChart.valueLabelFont = [UIFont fontWithName:@"HelveticaNeue-Light" size:9];
            self.lineChart.labelForIndex = ^(NSUInteger item) {
                return months[item];
            };
            self.lineChart.labelForValue = ^(CGFloat value) {
                
                return [NSString stringWithFormat:@"$ %.2f", value+lowFloat];
            };
            [self.lineChart setChartData:chartData];
            [view addSubview:self.lineChart];