Good Evening (or morning) everyone,

I have been trying to fit a non-linear regression line into my standard curve. However, I am getting the following error:

I have been using the following code:

```
stat_smooth(method= "nlm",
formula = y ~ a*x^b,
method.args = list(start = c(a = 470, b = 460)),
se=FALSE)+
```

I am not sure whether the value 'a' and 'b' are correct, as I have taken them from the regline equation code:

```
stat_cor(label.y = c(825),
label.x = c(0.88),
aes(label = paste(..rr.label.., ..p.label.., sep = "~`,`~")))+
stat_regline_equation(label.x=0.88, label.y=750)+
```

I have never been fitting a non-linear regression line. However, it is crucial in this experiment as I have got two variables only (concentration and the ratio) in a non-linear relationship.

This is the following code used

```
library(tidyverse)
library(tidyr)
library(dplyr)
library(readr)
library(ggplot2)
library(ggpubr)
library(gridExtra)
library(cowplot)
ggplot(data = STD, aes(x = Absorbance, y = STD)) +
labs(title = "Quantifying PGD2 in cell culture lysates and its enzymatic reactions ",
caption = "PGD2 ELISA")+
geom_point(colour = "#69b3a2")+
stat_smooth(method= "nlm",
formula = y ~ a*x^b,
method.args = list(start = c(a = 470, b = 460)),
se=FALSE)+
xlab(expression(paste("%B/"~B[0])))+
ylab(expression(paste("Prostaglandin"~ D[2], ~~ " MOX Concentration (pg/ml) ")))+
theme(plot.background = element_rect(fill = "transparent"),
panel.background = element_blank(),
panel.grid.major = element_blank(),
panel.grid.minor = element_blank(),
axis.line = element_line(colour = "black"))+
theme(legend.spacing.y = unit(0.01, "cm"))+
theme(legend.position = c(0.77, .91),
legend.background = element_rect(colour = NA, fill = NA))+
theme(plot.title = element_text(size = 12, face = "bold.italic"),
plot.caption = element_text(hjust = 0))
```

That produced the following outcome

Before that, I have added a line, but it is not a non-linear regression line tho.

Moreover, I have been thinking about whether the non-linear equation fits my graph, but it fulfills the legibility of the equation, so this is not the case.

Thank you so much for your help.