Send your .mdl file, the assignment brief, a screenshot of the exact error message and one line on what you have already tried. That way the session starts on the problem rather than on setup.
Get unstuck on your system dynamics model with a Vensim tutor who works through it with you on screen. Whether you are drawing your first causal loop diagram or debugging a model that will not run, sessions are built around your assignment and your deadline.
Personalized Vensim tutoring for stock and flow modelling, simulation, sensitivity analysis and coursework write-ups.
Every session is planned around what you need to understand next, whether that is a modelling concept, an error that will not clear, a simulation that behaves strangely or a report deadline this week. Learn live, share your screen, ask questions in real time and work at a pace that suits you.
Tutors Who Have Built Real Models
Work with tutors whose background is in system dynamics and simulation modelling, not just general software help. They know why your model behaves the way it does.
1:1 Live Vensim Support
Share your screen and fix the problem together in real time. Vensim support that follows your actual model file rather than a generic tutorial.
Coursework and Assessment Preparation
Strengthen your modelling, analysis and academic writing for reports, presentations and dissertations, within academic integrity guidelines.
Pick the area you are stuck on. Every item below is something students bring to a session, from a blank canvas to a model that runs but gives the wrong answer.
Turn a written problem into loops that actually close, and work out which are reinforcing and which are balancing.
Decide what is a stock, what is a flow and what is just an auxiliary. Most modelling problems start here.
Decide what stays inside the model and what becomes an input, so the model answers the question you were set.
Sketch the behaviour over time you expect to see before you build, then check whether your model reproduces it.
Model several regions, products or age groups without rebuilding the same structure by hand each time.
Lay out views so a marker can follow the logic, and keep the diagram readable when you paste it into a report.
Write stock equations correctly and set initial values that make sense for the system you are modelling.
INTEGAdd material and information delays, and choose between first and third order when behaviour depends on it.
DELAY1 · DELAY3 · SMOOTHShock the model on purpose to see how it responds, which is usually what the marking scheme is looking for.
STEP · PULSE · RAMPBuild non-linear relationships when the effect of one variable on another is not a straight line.
WITH LOOKUPStop stocks going negative, cap a rate at available capacity and switch behaviour on a condition.
IF THEN ELSE · MIN · MAXGet units consistent across the whole model so the units check passes and the equations mean something.
Units CheckTrack down the circular reference Vensim is complaining about and break the loop with the right stock or delay.
Work through a long units check error list and fix the cause rather than deleting the unit definitions.
Find the division by zero or negative stock that stops a run part way through the simulation.
Choose TIME STEP and the integration method so results are stable and not an artefact of your settings.
The model runs but grows forever or flatlines. We trace which loop is dominating and why.
Use the built-in tools to follow a variable back through the model instead of guessing at the problem.
Set up named runs, compare them on one graph and explain what each policy changed in the system.
Move a slider and watch the behaviour change, which is the fastest way to build intuition before you write anything.
Test which assumptions your conclusion actually depends on. Available in Vensim DSS, not in PLE.
Build custom graphs and get clean output into your report instead of low quality screenshots.
Run the standard structure and behaviour tests so you can defend the model in your write-up or viva.
Practise talking through the model in your own words so the analysis section is yours, not a description of the software.
Not sure which one your problem falls under? Send us the model file and the assignment brief, and we will tell you before you book.
Your session can focus on one urgent question or form part of a longer learning plan. Common areas of support include:
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Book your session, complete your secure payment via Stripe, and join your live, interactive lesson to begin your learning journey.
Leave with clearer priorities, suggested practice and the option to book further sessions.
Ideal for students needing help with basic or entry-level college material.
Tailored support for core and elective undergraduate courses.
Designed for master's level coursework and capstone projects.
Elite academic coaching for doctoral-level work and publications.
Tell us what you are modelling, where you are getting stuck and when you would like to meet. Send your model file if you have one. We will review your request and match you with suitable personalized live tutoring.
No guaranteed grades. No completed assignments. Educational tutoring only.
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Feedback from students we have supported on system dynamics and Vensim modules.
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It means a loop in your model has no delay in it, so a variable needs its own value to calculate itself. The usual fix is that something you drew as a stock is still typed as an Auxiliary, so changing it to Level and giving it an initial value breaks the loop. A tutor can trace which variable in the chain is the real culprit instead of you guessing one at a time.
Drawing a box does not make something a stock. The variable type has to be set to Level in the equation editor, otherwise Vensim treats it as an auxiliary that just looks like a stock on the diagram. This is one of the most common reasons a first model throws errors that make no sense.
The expression inside INTEG must equal your stock’s units divided by time, and the initial value must match the stock’s units exactly. A mismatch usually means a rate and a flow have been swapped somewhere, or a variable is missing a per-time unit. Deleting the unit definitions makes the error disappear but hides a genuine structural problem, so we fix the cause instead.
PLE does not support subscripts, and a model using them will open so you can see the structure but will not simulate. The same happens with functions PLE does not support. Running Model then Check will list exactly what is unsupported, and we can help you rework it or advise what version you actually need.
No. Monte Carlo and sensitivity testing require PLE Plus, Professional or DSS. If your assignment asks for sensitivity analysis and you only have PLE, that is worth raising with your module leader early, and we can show you what comparison runs can achieve in the meantime.
Each is a superset of the one before it. PLE covers basic stock and flow modelling, PLE Plus adds sensitivity testing and easier data handling, Professional adds subscripts and optimization, and DSS adds external functions and flight simulators. Tell us which one your university issued and the session will stay within what you can actually run.
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