I am working with testing data and there is a complication as to when the test is started. The data is recorded automatically and relates to engine RPM and oil pressure. The recording starts as soon as the engine is switched on but the test can actually start at some point later and this varies by several minutes per test.
We can see when the test starts as the RPM of the engine is raised to 1850 RPM, the first occurence of 1850 is when the 0 needs to be. I need to have this as the 0 point for the test with all other enties prior to this point to be negative and then positive after.