A mass spectrometry apparatus comprising: an ion source configured to generate ions; an ion guide configured to guide ions from the ion source towards a detector; the ion detector configured to detect ions; and a mass spectrometry controller configured to: generate a tune curve for the ion guide by varying the RF amplitude of the ion guide and measuring the peak area of a calibrant ion as the q of the ion changes with RF amplitude; determine an observed low mass cutoff for the ion guide from the tune curve; calculate an effective r0 for the ion guide based on the observed low mass cutoff, a nominal r0, and an expected low mass cutoff, wherein r0 effective is the calculated r 0 of the ion guide and the effective r0 is in accordance with the expression r 0 effective = K observed ∗ r 0 nominal 2 / K expected where r0 nominal is the assumed r 0 of the ion guide, K observed is the value for a parameter observed at a point in the tune curve and K expected is the value of that point when the tune table was created, the parameter being selected from q, q ∗ (m/z), q ∗ (m/z) ∗ ω 2, q ∗ (m/z) ∗ f 2, V, V/ω 2, V/f 2, or a combination thereof; determine an RF voltage based on the effective r0; apply the RF voltage to the ion guide; and perform a mass analysis of ions in a sample. an ion source configured to generate ions; an ion guide configured to guide ions from the ion source towards a detector; the ion detector configured to detect ions; and a mass spectrometry controller configured to: generate a tune curve for the ion guide by varying the RF amplitude of the ion guide and measuring the peak area of a calibrant ion as the q of the ion changes with RF amplitude; determine an observed low mass cutoff for the ion guide from the tune curve; calculate an effective r0 for the ion guide based on the observed low mass cutoff, a nominal r0, and an expected low mass cutoff, wherein r0 effective is the calculated r 0 of the ion guide and the effective r0 is in accordance with the expression r 0 effective = K observed ∗ r 0 nominal 2 / K expected where r0 nominal is the assumed r 0 of the ion guide, K observed is the value for a parameter observed at a point in the tune curve and K expected is the value of that point when the tune table was created, the parameter being selected from q, q ∗ (m/z), q ∗ (m/z) ∗ ω 2, q ∗ (m/z) ∗ f 2, V, V/ω 2, V/f 2, or a combination thereof; determine an RF voltage based on the effective r0; apply the RF voltage to the ion guide; and perform a mass analysis of ions in a sample. generate a tune curve for the ion guide by varying the RF amplitude of the ion guide and measuring the peak area of a calibrant ion as the q of the ion changes with RF amplitude; determine an observed low mass cutoff for the ion guide from the tune curve; calculate an effective r0 for the ion guide based on the observed low mass cutoff, a nominal r0, and an expected low mass cutoff, wherein r0 effective is the calculated r 0 of the ion guide and the effective r0 is in accordance with the expression r 0 effective = K observed ∗ r 0 nominal 2 / K expected where r0 nominal is the assumed r 0 of the ion guide, K observed is the value for a parameter observed at a point in the tune curve and K expected is the value of that point when the tune table was created, the parameter being selected from q, q ∗ (m/z), q ∗ (m/z) ∗ ω 2, q ∗ (m/z) ∗ f 2, V, V/ω 2, V/f 2, or a combination thereof; determine an RF voltage based on the effective r0; apply the RF voltage to the ion guide; and perform a mass analysis of ions in a sample.