diff dry is probably not numeric but character, it seems commas are used instead of full stop as the marker for decimal place, this is non standard., but you can replace the decimal, and convert to an actual numeric type.
somedata <- read_delim("Replica/Time/Diff dry (g)
1/-1/0,0034
1/0/0,0026
2/-1/0,002
2/0/0,0017
3/-1/0,0019
3/0/0,0064",delim="/")
plot(somedata$Time,
somedata$`Diff dry (g)`)
library(tidyverse)
somedata2 <- mutate(somedata,
`Diff dry (g)` = str_replace_all(`Diff dry (g)`,
",",".") |>
readr::parse_number())
plot(somedata2$Time,
somedata2$`Diff dry (g)`)